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A 100 liter freshwater aquarium

The aquarium (from the Latin aquarius "belonging to the water"; substantiated neuter aquarium : specifically "water container") is the most widespread type of vivarium . Most aquariums are containers made of glass or transparent plastic that are filled with water. Using fish and invertebrates such as molluscs or crabs as well as aquarium plants and soil materials, mostly gravel or sand, the aquarist (person who maintains aquariums) creates an underwater world and keeps it alive. Zoos that specialize in aquatic animals also refer to themselves as aquariums.

In the past, the cellar room in pharmacies, which was intended for storing liquid pharmaceuticals in bottles, barrels, etc., was called "aquarium". In England the term “aquarium” was then used to describe the basins set up in glass houses for the care of aquatic plants (but not aquatic animals). The modern term aquarium became common in the 19th century.

With fighting dogs are called activities that are associated with the operation of an aquarium and care of the living being held therein. The aquarium hobby is divided into the freshwater aquaristic and the saltwater aquaristic . This distinction is based on the salinity of the water used. The salt content in a brackish water aquarium is between that of a fresh water and that of a salt water aquarium.

Simple indoor aquarium (80 × 40 × 30 cm, 96 l)
Elaborate indoor aquarium (240 l)
Aquarium plants play an important role in the aquarium. They serve as protection for aquarium inhabitants, as a spawning point and enrich the aquarium water with oxygen; Echinodorus bleheri and Limnophila sessiliflora

History of the aquarium


Artificially created fish pond with tilapia on a wall painting of the burial chapel of Nebamun , around 1400 BC Chr.

The keeping of fish in an artificial environment has a long history. The Sumerians already kept caught fish in ponds before they prepared them for meals. Something similar is known from ancient Egypt. For all temple gardens from the early dynastic period to the New Kingdom, it is true that they were equipped with rectangular water basins , which were also used in hieroglyphic writing as single consonant symbols . Artificially created ponds and basins also played a central role in the often relatively small Egyptian house gardens. On an ancient Egyptian garden model that is now in the Metropolitan Museum in New York , the water basin framed by sycamore figs takes up almost the entire garden area. From images found at the Oxyrhynchus archaeological site , we know that fish were kept in such tanks.

Fish keeping in China is just as old . The targeted breeding of carp probably began around 2500 years ago; the oldest book on fish farming dates from 770 to 476 BC. During the Song Dynasty (960–1216 AD), goldfish were domesticated from the silver crucian , and from the early 16th century it is documented that goldfish were also kept in large ceramic vessels in houses. In 1596, the first book on the subject of the aquarium by Chang Chi'en-te was published with the title "Chu sha yü p'u", in German "Treatise on goldfish".

The first references to the keeping of farm fish in ancient Rome come from the 2nd century BC. At first there were freshwater basins in which farmers raised fish for consumption. At the beginning of the 1st century BC Commercial breeding of marine fish in seawater basins began by members of the upper class. Fish were soon held in it mainly for decoration. As a result, the seawater basins grew larger and larger and in the 1st century AD occupied large sections of the west coast of central Italy. Their business developed from the middle of the 1st century BC. A status symbol of an elite upper class. For about a hundred years fish farming became an integral part of the sophisticated Roman way of life, often with a tendency to waste. In the second half of the 1st century AD, the new Flavian dynasty demanded modesty and thrift. Subsequently, fish farming quickly lost its importance as a fashion.

The beginning of the aquarium hobby in Europe

The exact time at which living beings were first cared for in transparent containers cannot be precisely determined. The English diarist Samuel Pepys noted in his notes in 1665 that he had seen fish in London that were kept alive in a water glass. Most likely they were goldfish . Paradise fish , which came to London from Canton , where they were kept in garden ponds, through the trade relations of the East India Company are also mentioned . At first it was mainly natural science researchers who kept living things in containers in order to carry out their investigations. The British chemist Joseph Priestley, for example, who discovered oxygen in 1774 at the same time as Carl Wilhelm Scheele, who was working in Sweden from Stralsund , carried out more detailed studies on oxygen in aquatic plants that he kept in his laboratory.

Emil Adolf Roßäßler , "father of German aquaristics"
Salon aquarium from 1856

At the world exhibition in London in 1851 , aquariums were shown to the general public for the first time. The panes of these aquariums were held together by a cast-iron frame like a Ward's box .

The term "aquarium" , however, was coined by the English naturalist Philip Henry Gosse in his 1853 publication "A Naturalist's Rambles on the Devonshire Coast" . The book was very well received by the British public. A year later his book "The Aquarium: an Unveiling of the Wonders of the Deep Sea" was published . It became fashionable to keep living things in small glass containers, at least for a short time, so that they could be better studied. In Germany it was above all the natural scientist, educator and writer Emil Adolf Roßmaessler who made this hobby popular in Germany with various articles. He is therefore jokingly referred to as the "father of German aquaristics". In 1854 he published the anonymously published article Der Ocean auf dem Tisch in the then popular family magazine Die Gartenlaube . Similar to Gosse, he presented the care of marine animals here. With the publication, Roßäßler pursued the goal of making natural science known and popular among the people. He soon realized, however, that this was easier to achieve with a freshwater aquarium . That is why the article Der See im Glase followed very quickly in the gazebo , which led to so many inquiries about this form of animal husbandry that he published his book The Freshwater Aquarium in 1857 . In it, Roßäßler gave specific instructions on how to set up and maintain such an aquarium. In addition to the goldfish , he especially recommended the minnow and the mud whip .

Roßäßler's publications followed a large number of other aquarium books and magazines. Aquarium clubs were founded all over Germany. It became modern to set up a so-called salon aquarium or a goldfish bowl in the winter gardens of the Wilhelminian style villas .

Here the animals live just as they do in the wild - unlike the caged birds, reptiles and insects. Hindered and restricted by nothing, they show themselves to the observer in all their natural growth, in their full naturalness. (quoted from Horst & Kipper, p. 12) it was stated in an aquarium book published in 1880.

From today's perspective, this euphoric point of view is incorrect. At that time there was little knowledge about the needs of the creatures kept or the processes taking place in the aquarium. At that time, aquariums were sometimes still heated with candles that were placed under the aquarium. The fosterlings died very often in autumn because the water lacked oxygen and the aquariums were not adequately lit.

Controversial social discussions arose regarding the question of whether women should also breed fish within the aquarium hobby and whether only native species or "exotic species" should be kept.

Developments until today

The further development of the aquarium hobby over the past hundred years is mainly due to the understanding that an aquarium can usually not provide a habitat for fish and plants without appropriate technical and chemical support. The focus of further technical development was mainly in the second half of the 20th century . The decisive factor was next to a growing knowledge of the biological and chemical processes in an aquarium the availability of materials for the construction of increasingly sophisticated aquarium filters , improved lighting systems and smaller pumps and adequate purchasing power of a sufficiently large proportion of the population that was willing in this hobby to invest and inquire about such products . The topic is also spreading more and more in the communities .

Hammer Coral ( Euphyllia paraancora ) - Large Polyped, slow-growing corals can reach enormous sizes in saltwater aquariums.

Aquariums can be made of different materials. Until the end of the 1960s, most aquariums were frame aquariums, in which glass panes were cemented into metal frames and z. B. were sealed with bitumen , or full glass aquariums up to about 20 liters capacity. A decisive design change came with the development of silicone adhesives , which made the earlier metal frames superfluous. This made frameless aquariums in various sizes and shapes possible. The typical aquariums of the 1960s and 1970s were mostly clad with wood on the sides. This was to ensure that the aquarium fits harmoniously into the apartment. During this time, emphasis was placed on a harmonious diversity of plants in the tank, so that the Dutch plant aquarium was created.

There are various options and methods for setting the temperature in the aquariums. Contact thermometers, electronic control devices and manual temperature setting are common. Today, the rod heaters used in aquariums have measuring probes that enable adjustment to the degree without the need for additional devices. Electronic devices sometimes also allow time or daylight-controlled temperature control in accordance with the daily temperature fluctuations in the areas of origin of the fish. A gradual increase in water temperature, as it is necessary to trigger the readiness to spawn in some labyrinth fish , can be achieved relatively easily with electronic controls. Instead of rod heaters hung in the basin, there are also different types of floor heating. In large aquariums one often finds direct heating via heating coils that are controlled by the central heating.

The marine aquariums , which has long been operated by experienced aquarists is easier to implement today. However, it is still considered to be more demanding and also more expensive than freshwater aquariums. In practice, national preferences have emerged. In Germany and probably in many other countries, reef aquariums are mainly operated according to the Berlin system ; Many French marine aquarists use the Jaubert system, and the deep sand method has recently come from North America , which enables the enormous growth of hard corals with little use of technology. Zeovith method or algae refuge are further maintenance options in saltwater aquariums. However, none of them can be called the “best” system. Classic filters like those used in freshwater aquariums have not caught on.

Example of a nature aquarium in the style of Takashi Amano
Aquascape in Iwagumi style

Takashi Amano was one of the most influential aquarists in freshwater aquariums. He made the so-called nature aquarium popular, in which landscape images of nature are reproduced and which is significantly influenced by Japanese garden art . These are by no means biotope aquariums in which a habitat is reproduced exactly. Rather, the aim is to design aesthetic landscapes as objects of contemplation using the resources of aquaristics. Models from nature and imagination are transferred to the aquarium. Amano combined plants that come from different continents and socialized living beings whose habitats do not overlap in the wild.

A more recent trend in aquarium design, called aquascaping , is also moving in a similar direction . The focus here is on the attractive design of a water world, for example with plants. Often only very small fish or invertebrates are used, and in some cases animals are not used at all.

Nowadays there is an increasing variety of so-called "design aquariums". These tanks have the shape of a column or pyramid, or wall aquariums in the form of a picture or a hemisphere with insufficient volume are offered, which are not suitable for keeping fish (see goldfish bowl ). Designers invent pool facilities such as B. made of chrome elements or plastic hoses, which also fall under the aspect of cruelty to animals . The newest development of the aquarium shape is the bonsai aquarium . Here, similar to a paludarium, emphasis is placed on a part of the country that is designed with roots, waterfalls, moss and small solitary plants. The tank of this type of aquarium has a halved front and beveled side window.

Classification of aquariums

Freshwater aquariums can be classified according to a number of very different criteria. Nowadays, an important classification feature is the classification of water based on the substances dissolved in it. They are decisive for which organisms in the aquarium can be offered suitable conditions. In the past, more emphasis was placed on the distinction between cold and warm water aquariums.

Classification according to water conditions

Amazon basin with discus fish ( Symphysodon discus ) and red neon fish ( Paracheirodon axelrodi )

Aquariums are first differentiated mainly according to the salinity of the water. Seawater aquariums have the highest proportion of dissolved salt in the water. They simulate living conditions as they occur in the oceans. The salt content is 3.4 percent (34 g / l). In freshwater aquariums , the proportion of salt in the water is less than 0.6 percent. The living conditions in a lake or river are imitated. This type of aquarium is the most common in aquaristics . Brackish water aquariums , on the other hand, are a relatively less common type of aquarium. They simulate the living conditions of the estuaries of large rivers or mangrove coasts. The salinity is between the values ​​for a salt and fresh water aquarium.

Many tropical waters, from which the creatures kept in the aquarium come, have low-salt and very soft water. Names such as the Amazon basin or black water aquarium indicate freshwater aquariums that simulate these living conditions; However, while in a black water basin species of the most diverse origins are kept that require these housing conditions, in an Amazon basin only those plants, fish and invertebrates are kept that have their original range in the Amazon. So-called Malawi basins or East Africa aquariums mostly house fish from East African rift lakes with higher salinity. Aquariums for domestic cold water fish also often have harder water than those for tropical fish; however, the term "hard water basin" is unusual.

The so-called backwater aquarium is a specific type of aquarium . Here, a regular partial water change is dispensed with and only the evaporated water is filled with rainwater or distilled water. A relatively small stock of fish is necessary for this, so that bacteria (in filters , soil and biofilms ) and plants have the opportunity to convert the metabolic products that arise.

Classification according to temperature

Goldfish  - one of the species that can be cared for in the cold water aquarium

Most aquariums are tropical freshwater aquariums where the water temperature is kept constant between 22 and 28 ° C. Temperatures above 28 ° C are usually only in aquariums with extremely thermophilic fish such as discus or Loricariids to be found. Temperature fluctuations are limited (if at all) to a day-night rhythm or a slight increase or decrease in temperature during spawning time. There is no precise limit as to the water temperature from which an aquarium can be classified as a cold water aquarium . In general, aquariums are often referred to that do not have heating and are at room temperature. Depending on the location of the aquarium, it may even be necessary to use a cooling unit or room cooling to ensure that on hot summer days the water temperature does not rise above a level that is tolerable for the creatures being cared for. Larger fluctuations in temperature over the course of the year are characteristic of classic cold water aquariums. Fish species that are also native to the waters of Central Europe are often kept in them . These are for example Orfen , moderlieschen , loach , bullhead and the three-spined stickleback . Even the goldfish and a native of North America plate perch among the fish that feel good at not too high temperatures. In the last few decades, more and more fish from the subtropics and topographically high-lying regions of the tropics have found their way into cold water aquariums, e. B. various gobies and highland pennies.

Classification according to stocking

In Central Europe domestic Bullhead needed a flow tank

Most aquarists start with a so-called community aquarium , in which several fish and invertebrate species are kept that have the same conditions for the water values. For some fish species, not only the water values ​​play a role. The endemic cichlid species of Lake Malawi , known as mbuna , need rock structures that offer them caves and retreats. Most of the plants, however, are eaten by these fish. The rock pools in which these fish species are kept usually need good filtering, as the degradation of pollutants is not supported by aquarium plants. Similar to the rock pool, the current pool is also a type of aquarium in which specific environmental conditions prevail. This is where fish are socialized, which need a high flow speed of the water for their well-being. This is achieved by a powerful centrifugal pump having its outflow opening on one side of the basin, but its intake opening is relocated to the other side of the basin. Current basins in which streams are simulated and in which, among other things, brown trout are shown, can be seen regularly in large public show aquariums.

Species aquariums are especially common among more experienced aquarists who specifically care for and possibly breed a species that has special holding requirements. An example of such a fish species is the Australian goby , which feels most comfortable when the water temperature in the aquarium drops sharply during the night. Few other fish species can cope with these strong temperature fluctuations over a long period of time. Other species are not suitable for keeping in the community tank because of their aggressiveness towards other fish. The puffer fish that can be kept in freshwater or brackish water aquariums , such as woodlice , dwarf and palembang puffer fish, tend to pluck the fins of other fish. At least the first two species can possibly be kept together with very agile fish species, but a species aquarium is more recommendable for them.

Biotope aquariums are aquariums in which a natural habitat is reproduced as precisely as possible. Only fish from the same region are kept in such aquariums. Classically reproduced biotopes are a stream in the Amazon basin, a sour water pond in the Amazon basin, a Central American coastal stream, a West African river, a Lake Tanganyika biotope , a rocky coast in Lake Malawi, a Southeast Asian stream, a Southeast Asian irrigation canal, and a river estuary (brackish water) in Australia / New Guinea.

In the Japanese natural aquarium and the Dutch plant aquarium , aquarium plants play a role that is at least equal to fish species. Occasionally, the keeping of fish is completely dispensed with in Dutch plant aquariums. For both types of aquariums, fertilization with CO 2 is the rule to ensure optimal plant growth. Aquarium designs are often found that are based on a combination of features from the repertoire of Japanese, Dutch and German furnishing concepts.

Aquarium size

Europe's largest mobile aquarium
The front side

The smallest commercially available aquariums have a water content of only 4.5 liters. Aquariums with a capacity of less than 54 l are also known as nano aquariums . From approx. 30 l they are suitable for certain fish in very special cases. In them, however, mostly shrimp or other invertebrates are kept and - if it is seawater - also soft corals , crusty anemones , tiny crustaceans or echinoderms . Careful observation is important in such small aquariums.

The so-called ecospheres are even smaller, but in the opinion of many aquarists they do not come under the term aquarium. They are a closed glass body in which a dead coral, green alga and the shrimp species Halocaridina rubra are associated. This shrimp is so frugal that it can survive in these balls for up to two years without additional feeding (normal life expectancy 10–20 years). Intervention or feeding by the aquarist is not possible. For this reason, many aquarists reject this form of aquaristics.

The best-selling aquariums with the dimensions 60 × 30 × 30 cm hold 54 liters of water. These aquariums are also considered to be small aquariums, even if a number of fish species can be kept in them. In aquariums of this small size, care errors (such as in particular too high a stocking rate or a lack of partial water changes or incorrect feeding) have a much faster and more drastic effect than in larger aquariums. A rapid change in the pH value caused by incorrect maintenance can lead to the death of the living things being cared for in it. Aquariums with a capacity of more than 100 liters are therefore less demanding in terms of maintenance and are more suitable for the types of fish commonly used in aquaristics. Therefore, they are a useful size for less experienced aquarists. Prefabricated aquariums are available from specialist retailers with a volume of up to 700 liters. Custom-made aquariums can be significantly larger than this, even for private owners. However, the considerable weight of such an aquarium and its effect on the statics of a house must be taken into account.

The largest aquariums can be found in public show aquariums. Several show aquariums, such as the Shedd Aquarium , the Monterey Bay Aquarium and the Okinawa Churaumi Aquarium, have aquariums that hold 7.5 million liters of water.

The largest mobile aquarium in Europe holds around 60,000 liters of water and is shown at congresses or exhibitions, but can also be rented by private organizers. Mobile aquariums are difficult to supply not only because of the changing water quality at the individual locations, but also because an absolutely flat and stable subsurface must be available so that the centimeter-thick panes do not tear.

Components of an aquarium

A simple glass box is only seldom sufficient as a home for aquatic creatures. The environment at the source of the organisms at least replicate so well that they thrive and may even breed is in the hobby today on a large scale aquarium technology used.

Filters, lighting and heating


Schematic representation of an external filter system in the aquarium
Simple drawing / representation of an internal filter
Schematic representation of a mat filter
Simple drawing / illustration of a piggyback filter / backpack filter

A filter is usually used to maintain suitable living conditions (a filter is not absolutely necessary in a "run-in" aquarium with sufficient plants). Most fish species require heating and lighting. In addition, partial water changes are usually recommended.

Filters have the function of removing suspended particles, food and plant residues as well as dissolved compounds from the water or converting them into non-toxic substances. The aquarium filter in freshwater aquariums can be designed as an internal or external filter . Internal filters are the most common type of filter, but their use is mostly limited to smaller aquariums. One of the simplest filter forms is the Hamburg mat filter . External filters are now mostly operated as so-called pot filters; there are also sand filters or trickle filters , but they take up a lot of space. A special type of internal filter is the floor filter . The gravel from the ground is used as a filter. Such filter systems are uncommon in Germany and are mainly found in Great Britain and North America.

The degradation of pollutants takes place by microorganisms according to the principle of nitrification . In a new filter, however, the microorganisms are not yet present in sufficient numbers on the filter substrate. Newly set up aquariums are therefore operated for several weeks without fish stocking so that these microorganisms can establish themselves. This process can be accelerated by using so-called filter starters. Activated carbon filters, on the other hand, remove pollutants from the water in a physical way ( adsorption ); their absorption capacity is limited, which is why the activated carbon has to be renewed regularly.

Filter materials: peat balls to lower the pH value of the water, clay tubes and so-called "bio balls" for biological filtering, with foam in the background

In a saltwater aquarium , filtering is achieved using a protein skimmer . This is possible because sea water has a different surface tension than fresh water . Dissolved organic compounds, mainly proteins, but also fats and oils , accumulate at the interface between air and water. The creation of fine bubbles creates a more or less fine foam that can be removed from the aquarium along with the dirt. This process can also be observed on the coast when the sea surf produces foam that collects in the form of flakes on the beach.


When it comes to heating, rod heating with thermostat control is most common today. A floor heating is in either a heating pad placed on the bottom disk or housed a heating cable in the ground, is not necessary when setting up in heated rooms. One advantage of underfloor heating should be that the water circulates through the ground. A disadvantage, in addition to the higher purchase price, is that (unlike the rod heater) a simple exchange in the event of a defect is not possible. In the past, heating mats were often laid below the aquarium between the floor pane and the cabinet top. This type of floor heating has the advantage that there are no live parts inside the aquarium and the disadvantage that there is a great deal of heat loss because the heat from the heating mat first has to pass through the insulating floor pane. However, the risk of an electric shock is also averted with the internal heating mats or cables, as the common heating cable systems work with harmless low voltage.

Some external filters also have an integrated heater so that heated water flows into the basin; The result is better temperature control down to the last corner of the aquarium. Here, too, the disadvantage is that with such a combination device, the entire device has to be replaced if either the heater or the filter is defective. If the filter with integrated heating fails, the aquarium fish usually survive the deteriorating water quality for several days, but not necessarily the sudden drop in temperature.

For keeping animals from very cool waters, there are compact cooling devices that are integrated into the external filter circuit or have their own pump.


Fluorescent tubes are often used for lighting. The spread of mercury vapor lamps , also known as “HQL lamps”, is declining because metal halide lamps , also known as “HQI burners”, offer a higher luminous efficacy with the same output . HQI burners are recommended for pools over 50 cm high, as the light intensity decreases rapidly with increasing depth. These latter two lamps exude a special attraction through their point-like light emission (unlike the elongated fluorescent tube). This leads to the so-called caustic , especially when there is a strong surface movement of the water , as is known from diving.

In addition, a strongly moving water surface increases the loss of light by around half in contrast to a largely calm water level, which only causes around 20% light loss.

Fluorescent tubes specially tailored to the aquarium hobby enable the simulation of different lighting conditions (e.g. natural daylight, tropical sun, lighting with an increased blue component to simulate sea water depth). The choice of the illumination spectral colors influences the growth of aquatic plants (desirable) and algae (mostly undesirable). Tubes with an increased proportion of red and blue are specifically used to increase the visibility of the red, orange and blue tones of fish and corals, but they also promote algae growth. Most often, full-spectrum lighting is used, which creates color relationships similar to sunlight.

The use of electronic lighting controls enables the time-controlled setting of different lighting moods (color, brightness) and the simulation of sunrises and sunsets. As a rule, however, it is sufficient to control the lighting using a simple timer. If fish are kept, only a day-night change is necessary. Aquatic plants require a lighting period of 8 to 12 hours, which can be interrupted by a break in lighting.

The aquarium lighting is often integrated into the aquarium cover. It must be able to withstand the prevailing damp room conditions and exclude the risk of electric shock when working on the aquarium. In order to avoid unnecessary and considerable energy losses through evaporation, an aquarium cover is generally used if the aquarium is not operated in the open (with the possibility of marsh plants growing out).

For aesthetic reasons, but also to observe the behavior of nocturnal animals, moonlight lights are also used, which simulate a faint bluish moonlight after the main lighting has been switched off. This effect lighting is realized with LEDs or cold cathode tubes of low power. The effect on the nocturnal behavior of the fish is controversial. On the one hand, absolute darkness is unnatural and can cause stress in the animals, on the other hand, too bright "moonlight" can prevent the animals from calming down. There are isolated reports of improved spawning behavior under moonlight lighting.

LED tubes can now replace T8 fluorescent tubes to some extent. In the case of T8 fluorescent tubes, replacing them with T5 LED tubes is only conditionally recommended, as the tube diameter is significantly smaller than that of T8 and there is not a lot of space available for heat sinks inside the LED tube, so that the overall output of the T5 tubes is high is limited. You also have to note that there are LED replacement tubes that continue to be operated with the transformer of the fluorescent lamp, where only the starter has to be replaced by a bridge. With these "retrofit tubes" you have to consider that the efficiency does not come close to the tubes that are operated directly with 230 V, so the cabling has to be changed on the socket beforehand, in which the old transformer is completely excluded from the electrical circuit . For this reason, fully wired LED light bars have become established, which no longer have much in common with the original light bar and fluorescent tube design, but can be easily integrated into covers without having to make electrical changes.

Although aquatic plants need the entire light spectrum for their photosynthesis , they mainly use the red (around 700 nm) and blue (around 450 nm) spectral range. White light-emitting diodes also emit in this spectral range.

More equipment

A thermometer is necessary to check the water temperature occasionally. Thermo foils are also available, which are stuck on from the outside at a point on the aquarium glass. These thermometers, which show the temperature by means of different colors of the writing, are less precise.

Fish or free-floating plant components are fished out of the water with a landing net or a fishing bell. A fishing bell is particularly suitable if the fish are very sensitive or you want to catch schools of young fish. A hose and bucket are required to change the water. A gravel cleaner helps to sludge removed from the aquarium. If you are absent for a longer period of time, it makes sense to have an automatic feeder that regularly dispenses food into the aquarium over a longer period of time. With it, the supply of the fish is ensured during a vacation. Long - handled tweezers , scissors or a sharp knife and hands can be used to care for the aquarium plants . A spawning box is often used to prevent viviparous fish in the aquarium from eating their offspring after spawning .

Some electronic devices are available for determining the water values. But there are also easy-to-use immersion and drip tests. During immersion tests, test sticks are briefly dipped into the aquarium water. The value to be determined can then be measured using a color scale. Dipping tests are available in stores that simultaneously determine nitrite , nitrate , total hardness , carbonate hardness and the pH value . They are occasionally criticized by aquarists for their inaccuracy. The easiest way to estimate the carbon dioxide dissolved in the water is with a CO 2 long-term test . The drip tests also measure the substances contained in the water using a color scale. A certain number of a test solution is given to usually five or ten milliliters of aquarium water. For most aquarists, the drop tests are reasonably accurate.

Tap water and aquarium water

Hobby aquarists often opt for a stocking with creatures that can cope with the water conditions that the respective tap water offers. If the water values ​​of the aquarium are also available for tap water, an aquarium can then be filled directly with tap water at the appropriate temperature after a partial water change. However, many aquarists treat the water with a water conditioner in order to bind the heavy metals in it and to neutralize any chlorine that may be present . Filtering with an activated carbon filter is only necessary if the water is very heavily contaminated with heavy metals or herbicides . The nitrates produced in the biological nitrogen cycle can be removed with a nitrate filter if necessary .

In general, tap water can be changed so that any desired water value can be achieved. Very hard tap water can be brought to the desired lower degree of hardness through reverse osmosis or a mixed-bed filter. Brackish water or salt water conditions are achieved by adding special mixtures of salts.


Most aquariums have a substrate consisting of gravel or sand with no significant lime content. Quartz gravel or sand, which has no chemical influence on the water quality, is particularly suitable for aquariums. Calcareous rocks harden the water.

Gravel is most commonly used as a substrate. It is available in different grain sizes. Round cut stones are recommended so that fish with sensitive barbels cannot injure themselves. It is also advisable if the gravel height is lower at the front than at the back. Plant remains etc. slide forward. This is an advantage as you can easily remove the plant debris. The size of the gravel depends on the creatures to be cared for. In general, there is a risk that if the gravel size is too large, food residues will fall into the stone gaps, where the fish cannot reach them and rot in the gaps, which negatively affects the water values. Small gravel sizes with a diameter of around one millimeter are necessary for freshwater shrimp , for example . The animals are then able to turn the individual stones with their legs and search for algae growth. Aquarists who value good plant growth sometimes bring organic material (special aquarium potting soil, potting soil, garden soil or sheep droppings) below the gravel layer in order to provide the plants with sufficient nutrients. Other aquarists refrain from doing so, as ground-burrowing snails can dig up this potting soil. Instead, they put fertilizer balls or sticks in the gravel directly below or in the vicinity of the plants. The color of the gravel is in large part an aesthetic choice. However, fish that are kept in aquariums with very light gravel as the substrate appear paler. In the case of fish species that come from shady habitats, a substrate that is too light can trigger scrubbing behavior.

For a few fish species, sand is necessary as a substrate to accommodate their burrowing hiding place. It makes sense that it should not have too high a fine fraction in order to prevent water clouding and caking. A single-grain grading curve is helpful. The grains of sand should be rounded and not sharp-edged so that bottom-dwelling and bottoming fish do not injure themselves.

Decoration material in the aquarium

The partner goby (
Amblyeleortis guttata ) should only be kept in pairs and together with the shrimp Alpheus bellulus or A. ochrostiatus .

Aquariums are often decorated with stones, empty mussel shells and bog roots . The use of this decoration material not only serves the aesthetic satisfaction of the aquarium owner, but is also often necessary for the creatures cared for in the aquarium. For example, many cichlids are cave breeders and only lay their spawn on the top of a stone cave. Catfish grate the wood of the Moorkienwurzeln and shrimp of the genus Caridina prefer to look for small algae growth. Some species of fish, such as the Tanganyika snail bass , rely on their aquarium to offer them empty snail or mussel shells as a place of retreat. And finally, like aquatic plants, such decorative objects mark territorial boundaries for territorial species.

When choosing the decoration material, it is essential to ensure that it does not release any toxic substances into the aquarium water even after long periods of watering or that the water values ​​do not change the water values ​​for the species being kept. Unsuitable stones can e.g. B. release mineral salts, iron or lime.

Energy demand and energy saving


Energy is primarily used for heating, lighting and water treatment.

In the following energy consideration, a standard aquarium (200 liters) of 100 cm × 40 cm × 50 cm (L × W × H) with a cover should serve.

Power consumption of consumers
consumer Power [W] Duration [h] Work [kWh / year] Proportion of [%]
pump 10 24 87.6 20th
heater 100 3 109.5 25th
light 64 10 233.6 55

In total, this makes an annual consumption of 430 kWh, which is about a quarter of a single household (around 1800 kWh). As a rough estimate, one can assume about 2 kWh per year per liter.

Energy losses

Heat loss

At 47%, the heating of the aquarium is the most energy-consuming consumer. Two essential factors are decisive here:

  • Heat loss through thermal conduction of the glass:

In this regard, the surface available for heat exchange, the temperature difference between the water and the surrounding room air and the heat transfer coefficient or U-value are important . The heat transfer takes place approximately on the cover and the side walls, the floor is usually already somewhat insulated and should be neglected in the consideration. A temperature difference of 5 K (25 ° C water temperature and 20 ° C room temperature) is assumed.

Heat loss through conduction
material U-value [W / (m²K)] Area [m²] Delta T [K] Power [W]
Glass 1 cm without insulation 7th 1.1 5 38.5
Glass with 3 cm WLG 035 insulation 1 1.1 5 5.5

A high temperature difference as well as a large heat exchange surface ensure high energy losses.

  • Heat loss through evaporation

Evaporation, also known as evaporation , permanently removes energy from the water, which, as with the heat transfer mentioned above, has to be replenished by heating. Now, by attaching an aquarium cover, the exchange of air and thus moisture can be reduced significantly. The air below the cover is saturated with water and cannot absorb any more moisture and thus suppresses evaporation. However, a cover will not and should not be airtight, which is why evaporation will still take place, but to a significantly limited extent.

The following example calculation makes this clear. Assuming natural convective air exchange without an aquarium cover, a water loss through evaporation of around 5-6 liters per day per square meter of water surface can be assumed. With a lid this is reduced to 1–2 liters per day. At a water temperature of 25 ° C, around 2441 kJ per kg of water are lost (corresponds to 0.684 kWh per day per liter of water).

Heat loss through evaporation
Power loss [W / m²]
without cover 155
with cover 42

Light output

Depending on the light source used, the energy efficiency is correspondingly good (see lighting ). In the case under consideration, light accounts for 38% of the energy. The use of LED lights would reduce the energy requirement to around 90% (approx. 20 watts) with the same light output. It must also be taken into account that there is no heat source due to the design.

Total energy losses

In practice, it depends very much on the size of the aquarium and the technology used. The main part of the energy losses is caused by the heat losses to be compensated and the lighting. In an aquarium with a volume of 500 liters (gross), energy consumption values ​​of approx. 2-3 kWh / day are measured.

Living things in the aquarium

Aquarium plants

As aquarium plants are plants called that can live in different aquariums types. These are aquatic plants that always grow submerged (“under water”) in their natural habitat , or marsh plants that grow emersed (“above water”) and live submerged under natural conditions at least for a certain period of time.

Aquarium plants played no role in early aquaristics. The fishbowl , which is now rejected as cruelty to animals, was made without any vegetable contribution. In the 20th century, however, it became clear that a well-functioning aquarium also required a sufficiently large number of plants. Individual types of aquariums, for example some cichlid tanks or rock pools , are an exception. Plants that thrive optimally can improve the quality of the water in the aquarium by breaking down or absorbing pollutants such as too much phosphate , too much nitrate and too much ammonium . With the "harvesting" of aquarium plants, such pollutants as well as heavy metals and other toxins are removed from the aquarium. The aquarium plants produce the oxygen used by the living things in the aquarium for breathing by means of photosynthesis during the lighting phase of the aquarium. Plants also reduce unwanted algae growth in the aquarium by removing nutrients from the algae when they are growing well. Fish are mostly dependent on plants for their well-being. You need them as hiding places, as oxygen producers , as territorial boundaries within an aquarium and as a spawning area. In the natural aquariums , as propagated by the influential aquarist Takashi Amano , and in the Dutch plant aquariums , plants even play a leading role.

According to estimates by the aquarium plant expert Christel Kasselmann , between 100 and 150 plant species are offered as aquarium plants . Only 30 species are real aquatic plants.

When designing the aquarium, a distinction is made between floating plants, foreground plants and solitary plants. Plants that can be used as floating plants in aquariums are those that basically float on the surface, as well as plants that are able to absorb the necessary nutrients through the water column and therefore do not have to be rooted in the soil. The number of aquarium plants that remain small enough to be used as foreground plants is not very large. In larger aquariums, plants with a height that would be annoying in the foreground in small aquariums can also be used for this purpose. Many aquarists plant a large plant as a visual highlight in their aquarium. Plants from the genus of sword plants are particularly often offered as solitary plants, the cultivars of which often have red-brown or conspicuously spotted leaves. Occasionally it is also recommended to plant solitary plants to the right or left of the center (see golden ratio ).

The typical Dutch plant aquaria plants roads are with plants such Bachburgel , Cardinal Flower and moss balls achieved. Owners of these aquariums often try to cultivate particularly demanding aquarium plants such as tongue leaf , cognac plant , water hair and milfoil . In the Japanese natural aquarium, small and dainty species that are planted in the foreground often play a role. These include the pond liver moss , the tongue leaf and the needle ledges . In these types of aquariums, plants such as Java fern are often tied to stones or roots. In aquariums with fish that eat tender plants, the dwarf pear leaf in particular has proven its worth, the hard leaves of which are rarely damaged by any fish species.

Carbon dioxide (CO 2 ) , which plants need for their growth, is only dissolved to a small extent in water and comes from the bacterial decomposition of organic material such as dying plant parts or leftover fish food. The need for carbon dioxide differs depending on the type of plant. There are a number of aquarium plants, such as the dense leaved waterweed , the Indian water friend and the Indian water star , whose CO 2 requirements can be ensured without additional supply. In addition to a whole range of aquarium plants that are also suitable for a newly set up aquarium, all three types of plants are often recommended. Because they grow well and are fast-growing, they effectively deprive the algae of their nutritional basis in the initial phase of an aquarium, when the risk of excessive algae growth is particularly high.

Many aquarium plants need a higher carbon dioxide content in the water in order to thrive. These plants are dependent on carbon dioxide fertilization , which should achieve a CO 2 content of at least 20 mg / l. There are a number of different ways of achieving this fertilization. This ranges from a fermentation system based on alcoholic fermentation (yeast fermentation) to chemicals that release carbon dioxide in the aquarium water and a (possibly computer-controlled ) pressurized gas cylinder system.

Strong surface movement of the water and the use of air stones (air stones) drive out the carbon dioxide dissolved in the water to a large extent. Believing that they can bring more oxygen into the water for the fish, the opposite is achieved through membrane pumps and splashing filter inlets: The carbon dioxide dissolved in the water is increasingly released into the air via the water surface and deprived of the aquatic plants as a basis for life, which then grows less react, generate less oxygen and leave more nutrients to the algae. Therefore, contrary to popular opinion of beginners, aquarium water rich in carbon dioxide is not poorer in oxygen, but richer in oxygen.

When equipping the aquarium, it must be taken into account that there are aquarium plants with higher maintenance requirements, some of them problematic plants, which have higher requirements for keeping them (for example, plants that need a lot of light, extreme requirements for water hardness, high requirements for the concentration of water constituents, special Temperature conditions) and those with low maintenance requirements, which thrive without additional carbon dioxide fertilization and are particularly suitable for the initial planting of an aquarium.

Almost all of the aquarium plants available in stores come from nurseries that specialize in the breeding of aquarium plants. Especially from the genus of sword plants , new varieties are used again and again, which are characterized above all by interesting red to reddish-brown speckled leaf colors.

Aquarium plants can also multiply in the aquarium (for example through runners on which offshoots arise, or through self- branching of the shoot axes ) or be reproduced (for example through rhizome division or by using young plants sprouted from shortened stem plants; propagation via flowers and seed attachments is only possible with Water lily plants ).

Excess plant growth can be responded to by plucking leaves or shortening stems.


The discus is considered by many aquarists still considered the "king of fish"
Blue Congo tetra are usually kept in a tropical community tank
Siamese fighting fish , male - they were first bred in Europe in France in 1893

The first fish species kept in European aquariums mostly came from local coastal and inland waters . The goldfish is one of the few foreign aquarium fish that was mentioned very early in the aquarium literature . One of the first strikingly colored tropical fish to be imported regularly and in a targeted manner was the paradise fish . It is documented that it was first held in Germany in 1876. This species was one of the few fish that could survive the long journey from Asia. Paradise fish are not only dependent on gill breathing , but as labyrinth fish are also able to breathe atmospheric oxygen via their so-called labyrinth organ .

Due to the demand in Europe, other types of fish followed very quickly, imported from regions such as Manaus in Brazil , Bangkok in Thailand or Jakarta . Most of them were labyrinth fish like the paradise fish. Due to the lengthy transport, however, initially only those fish species prevailed in the aquarium hobby that could be bred. The majority of the fish commercially available today come from bred fish. However, wild- caught fish are still offered on a regular basis, as some fish species can still not be bred in captivity or their catch is more economical than breeding. New species have also been introduced into the aquarium hobby through wild catches. This applies in particular to armored catfish , cichlids and tetras .

Like many other hobbies, dealing with the keeping of living things in aquariums is subject to trends and fashions. In freshwater aquaristics, many aquarists still consider the discus the “king of fish”. The keeping of angelfish and the so-called mbunas is also very popular . Many aquarists also keep catfish , with a strong demand especially for species that have an unusual body shape, such as the large-head frying pan catfish or the blue antenna catfish . In the case of some newly introduced catfish species such as the very strikingly colored zebra fish, this demand is also expressed in a high price compared to other fish species.

According to their diet, fish can be divided into piscivorous piscivores , insectivorous insectivores , herbivorous herbivores and plankton eaters . Usually the position of the fish's mouth suggests which food niche each species uses. Fish with an upper mouth are usually fish that eat on the surface of the water. A lower mouth can usually be found in bottom fish that look for food in sludge or on stony ground or peel off algae growth .

The animal feed industry now offers a wide range of ornamental fish feed for feeding the fish . Dry food , which is offered in flake, granulate or as food tablets, is available in different compositions to meet the different nutritional requirements of the individual fish species. However, not all fish species accept dry food. Water fleas , mosquito larvae , river flea shrimp and other small aquatic animals are primarily used to feed primarily predatory fish species. These feed animals are offered live, dried, freeze-dried or frozen (" frozen food "). Types such as B. Archer fish are absolutely dependent on live food . Live food such as grindal worms and brine shrimp can be grown yourself. However, the trade offers a range of feed animals.

Invertebrates and amphibians

Apple snail , which with its Sipho takes a breath

In recent years in particular, the targeted keeping of invertebrates has increased in freshwater aquariums . It has been practiced for a long time in saltwater aquariums.

Tower snails and ramshorn snails have been found in aquariums for a long time. The burrowing tower snails in particular aerate the soil and utilize organic plant matter. Although they ensure healthy plant growth in this way, they have always been more of a "support" in the aquarium hobby. The trade is also offering more and more strikingly colored or shaped snails such as the different species of apple snails or the zebra snail . Because of their high metabolism, they must be included in the maximum number of animals that can be kept in the aquarium. The minimum edge length for an apple snail is 60 cm.

For some years now, freshwater and rock shrimp have been kept in freshwater aquariums. Their popularity is mainly due to the Japanese photographer and aquarist Takashi Amano , who used Yamatonuma shrimp in his aquariums to control algae. This has led to the increased introduction of other types of shrimp .

Some types of cancer are also commercially available. In freshwater aquariums, it is mainly the crayfish species that belong to the fauna of Australia or North America. These crabs, similar in habit to a lobster, are mainly bred on farms for food. Blue-colored specimens such as the yabbi , the marron and the red claw lobster are particularly popular in pet shops . All three species require very large aquariums, can only be kept with large fish and also attack the aquarium plants. That is why the tiny orange pygmy crayfish is also popular . Crabs, on the other hand, are rarely kept in pure aquariums; With a few exceptions, they always need a sufficiently large area of ​​land for their well-being and are therefore kept in aquaterrariums .

Amphibians are rare pets in the aquarium . The species that are more frequently kept in the aquarium include clawed frogs , dwarf clawed frogs , the Japanese fire-bellied newt , the axolotl and the swimming burrows .

Unwanted organisms in the aquarium


Guppy  - they are among the fish that eat algae growth
Shell flowers remove nutrients from the water and thereby reduce algae growth
The Yamatonuma shrimp is also used to combat algae in the aquarium

Algae spores are only a few micrometers in size. They are brought in when fish and plants are moved and put in, and when the water is changed. If they multiply explosively, this is an indication that the nitrogen conversion in the aquarium is not working sufficiently well.

The so-called beard and brush algae belong to the red algae . They are a dirty green to blackish color. The red color, which gives it its name, is visible when the algae threads are placed in alcohol. Red algae are eaten by a number of fish species. Diatoms occur, among other things, when an aquarium is only inadequately lit and the oxygen content is too low due to the then low assimilation performance of the aquarium plants. These algae, which form a smeary, brownish coating on stones and roots, disappear when the lighting conditions in the aquarium are improved. Green algae , on the other hand, have similarly high demands on the water as aquarium plants. They are green to light green in color and, depending on the type, grow like cotton wool, thread-like or tuft-like and can be easily removed by hand or tweezers.

Particularly in the initial phase of an aquarium, so-called blue - green algae (cyanobacteria) can multiply strongly, which usually form a blue-green, occasionally blackish-purple or brownish coating over plants and stones. Blue-green algae grow very quickly and can suffocate plants that have not yet grown well. Mechanical removal makes sense, but even the smallest residues can grow back in large quantities.

Measures against algae

An excessive growth of algae in the running-in phase of an aquarium can be prevented by waiting several weeks before the aquarium is filled with fish and invertebrates for the first time. During this time, the aquarium is illuminated for about ten hours a day, and the filter is already running continuously. At the same time, the aquarium is planted very densely with fast-growing plants. The plants deprive the algae of the nutrients necessary for their explosive growth, and during this time the microorganisms that are necessary for the conversion of ammonium , phosphate and nitrite can settle in the filter . New filters can be inoculated with special bacterial cultures from specialist dealers in order to stimulate biological activity. When the filters are run in, all filter media should never be changed / cleaned at the same time, so that the colonized bacterial cultures are not completely destroyed. If you already have an aquarium, you can replace some of the fresh water in the new aquarium with aquarium water and put some filter sludge from the inserted filter into the filter of the new tank. This helps in the running-in phase to form a new equilibrium more quickly. Beginners in particular confuse well-meaning “sterility” with biological cleanliness, which is produced less by mechanical filtering and “fresh” water than by active microorganisms in the substrate and the coarse-pored filter media.

The majority of aquarium plants are marsh plants that are grown emersed in water nurseries . You therefore need a few days to adapt to the aquarium environment. The recommended plants, which grow very quickly even with previous emersed cultivation, include Indian water friend and water star . Dense leaved waterweed is also very suitable; it is cultivated submerged, but requires strong lighting. It can grow both flood and rooted; The native horn leaves are almost always flooding and also contribute to a reduction in nutrients in the aquarium. The same applies to floating plants such as mussel flowers and duckweed .

A number of fish species eat algae. The Siamese trunk barbel and the beautiful-finned trunk barbel are excellent algae eaters . Also otocinclus and ancistrus be maintained, among other things because of this characteristic in the aquarium. Often held by beginners guppies and Spitzmaulkärpflinge to the cultivar Black Molly heard are, eat fish which caused algae nursery. An existing algae plague can hardly be combated by algae-eating fish, as these animals mainly graze on young, tender algae. Despite their reputation for destroying algae, snails are not very suitable, as they can develop into a plague through proliferation and contribute to fertilization themselves through their metabolic products. In addition, it is freshwater shrimp that effectively counteracts the growth of algae. The trade also offers chemical agents against algae growth. However, these agents also damage the plants, even if, with a delay of weeks or even months, since plants have a smaller effective surface area than algae.

Filamentous green algae (thread algae), which often appear in the running-in phase of an aquarium, can be collected daily and then usually disappear again.

UV lamps can be installed in the water circuit of an external filter against floating algae.

If the aquarium is infested with cyanobacteria, switching off the light and darkening for eight days after a water change of around 50% can help.

Snails and planarians

Although snails have an important function in the aquarium, some species can reproduce very quickly and get out of hand in the aquarium. They often become a nuisance when the fish are fed too abundantly, so that the snails find a very large food supply. They can be removed using special snail traps. Some fish species also eat young snails, although it must be noted that the snail-eating fish, which are often recommended, have special requirements that cannot be achieved in many aquariums (e.g. loach can be up to 30 cm long and require several conspecifics and require an aquarium with a minimum edge length of 150 cm).

Planariums also occasionally appear in aquariums. These are worms up to several millimeters in size that crawl around on panes and furnishings. While they are not dangerous to adult fish, they can eat the fish spawn. Planarians multiply particularly when there is plenty of leftover food and organic waste in the aquarium. Chemical agents that treat planarians also make snails and possibly plants die. It can be helpful if the aquarium has a water temperature of at least 35 degrees Celsius for several days. During this time, the fish and “desired” invertebrates must be kept in a replacement aquarium.

Chemistry in the aquarium

PH value

The scalar needs a pH value between 5.5 and 6.5 for its well-being.

The pH value is an important "water value" in aquaristics. It expresses the relationship between the acidic and alkaline components of the water; more precisely, the ratio of hydrogen ions and hydroxide ions. If there is an excess of hydrogen ions, one speaks of an acid, if the hydroxide ions predominate, one speaks of a base. Living organisms have a differently large tolerance range for the pH value and cannot survive outside of this in the long term. Checking whether an animal species finds suitable conditions for survival in an aquarium is based, among other things, on the pH value.

The pH is measured on a logarithmic scale with values ​​between 1 and 14. Water values ​​in the aquarium are between 4.5 and 9.5, both of which represent extreme values. A pH of seven is considered to be “neutral”; H. neither as alkaline (basic, pH value> 7) nor as acidic (pH value <7). Logarithmic means that water with a pH value of six already contains 10 times more acids than water with a pH value of 7. Water with a pH value of five already contains 100 times more acids than water with a value of 7. So-called black water aquariums , in which South American fish such as angelfish or the frequently kept red neon thrive, have pH values ​​in the range of 5.5 to 6.5.

Most aquatic plants thrive best in water with a pH value between 6.2 and 7.2, as these values ​​usually also have a higher carbonic acid content, which is important for plant growth . East African cichlids in particular feel good in water with a pH value above 7 .

There are various ways to measure the pH value:

1. pH test strips or indicator paper: the solution to be measured is dripped onto such a test strip or indicator paper or the test strip is immersed in the water to be examined. The discoloration is compared with a table to determine the pH. This is an easy and quick way to measure pH, but it is relatively imprecise.

2. pH drop test: In this measuring method, drops of a reagent containing an indicator are added to a certain amount of a solution to be measured, and the discoloration is also compared with a table. This measuring method takes a little more time and is usually a little more expensive, but also much more accurate than measuring with indicator paper.

3. Electronic measuring device: Here an electrode is dipped into the solution to be measured and an electronic display device determines a pH value from various factors. The advantage of this measurement method is that the solution can also be discolored or otherwise contaminated.

Carbonate and total hardness (acid capacity and hardness)

The carbonate hardness (KH) describes the amount of carbonate and hydrogen carbonate ions. So that these anions can function as carbonate hardness builders, a corresponding number of calcium and magnesium cations must be present. The carbonate hardness represents an acid buffer in water, which prevents a strong and rapid change in the pH value. The carbonate hardness is therefore referred to as the acid capacity (acid binding capacity up to pH 4.3). Water with a low KH value generally has a low pH, while water with a high KH value is usually alkaline.

The total hardness (GH), also called hardness , denotes the sum of all ions of the alkaline earth metals dissolved in the water . In addition to magnesium and calcium (approx. 80%), these include strontium and barium . In the aquarium hobby, the total hardness usually plays a smaller role than the carbonate hardness. Usually the carbonate hardness is lower than the total hardness.

Instead of the newer terms acid capacity and hardness, the established terms carbonate hardness and total hardness are mostly used in aquaristics. It should be noted that an acid capacity of 1 mmol / l corresponds to a carbonate hardness of 2.8 ° dH and a hardness of 1 mmol / l corresponds to a total hardness of 5.6 ° dH.


The conductivity (wrongly for the electrical conductivity measured at 25 ° C in µS / cm) depends on the sum of all dissolved salts in the water. The more salts are dissolved in the water, the better the conductivity. Fully demineralized water hardly conducts any electricity (low conductivity is always given due to self-dissociation ).

The conductance plays a role in particular when soft water fish are to be bred.

Salinity and redox potential

A determination of the salinity and the redox potential is only required for brackish water and sea ​​water aquariums .

The density of the salt content is measured with a hydrometer . Fresh water has a specific gravity of 1.0 at a temperature of 4 degrees Celsius. Tropical sea water, i.e. sea water that is normally reproduced in a sea water aquarium, has a specific gravity between 1.020 and 1.027 at this temperature because of the dissolved salts and trace elements. Brackish water lies between these two values. The hydrometers used in the aquarium hobby are calibrated to 24 degrees Celsius.

The redox potential says how much the water is contaminated with organic substances and what oxygen content it has. High values ​​indicate a high oxygen content and a low content of organic substances. The redox potential is measured with electronic measuring devices. When determining the values, the pH value and the water temperature must also be taken into account.

Nitrogen conversion in the aquarium

Nitrogen cycle in the aquarium

Plants need nitrogen as a nutrient. The aquarium plants have ammonium (NH 4 ) and nitrate (NO 3 ) available as nitrogen sources. Other nitrogen compounds in the aquarium water are urea as well as nitrite and ammonia, which are toxic for fish . Nitrite and ammonia can be converted into non-toxic nitrate by bacteria , which is referred to as nitrogen conversion or nitrification .

This nitrogen conversion, which takes place in the aquarium (and in the aquarium filter) by plants and microorganisms, is also known as the nitrogen cycle. In very few aquariums, however, there is actually a cycle in which interventions are no longer necessary. The living things in the aquarium are usually dependent on food. Regular partial water changes are used to reduce nitrate .

The toxic ammonia is initially released through the gills and from the urine of the creatures cared for in the aquarium as well as the unused food . In water that is not too alkaline, this nitrogen compound is mainly present as ammonium . This is less harmful to the fish and invertebrates in the aquarium. For plants it is even a fertilizer. Ammonia predominates only at high pH values ​​and temperatures. Ammonia is a strong poison for fish. If ammonia is highly concentrated in the water, they are no longer able to breathe ammonia through the gills.

The ammonium that is not consumed by the plants as a nutrient is used by microorganisms such as B. Nitrosomonas bacteria, which are present in both the aquarium and the filter, are broken down into nitrite . Like ammonia, nitrite is poisonous for fish and fatal from values ​​of 1 milligram per liter. Sudden shooting of the fish in the aquarium, apathetic behavior or hectic breathing indicate possible poisoning by nitrite. Nitrite is, however, by z. B. Nitrobacter bacteria are converted to nitrate in the next stage. This process, in which ammonium is converted into nitrate with consumption of oxygen, is known as nitrification . Nitrate is not toxic to fish, but in high concentrations it can damage the aquarium plants. It should be kept low in order to avoid (partial) denitrification (see below) in the aquarium or the body of the fish, which would ultimately release nitrite again. Nitrate is therefore removed from the aquarium water by regular partial water changes. In addition to nitrification, there is another process in which microorganisms inhale nitrate as a substitute for oxygen. This anaerobic process is known as denitrification . It rarely occurs in most aquariums. For the removal of nitrate z. B. a special nitrate filter can be used.

If the nitrate content of the water is too low (below about 0.5 mg / l), plants can be damaged - just as if the content is too high. A nitrate deficiency can cause symptoms similar to an iron deficiency in aquarium plants.

Other chemical substances relevant for the aquarium

The presence of macro and micronutrients is essential for aquatic plants .


  • Carbon: Plant building material, absorbed from carbon dioxide. Some aquarium plants, especially sword plants, can (if there is too little carbon dioxide in the water) obtain carbon from hydrogen carbonate ions. During this process, called biogenic decalcification , crust-like deposits of lime, which is a “waste material”, are deposited on the photosynthetically active leaves.
  • Phosphate : Plant nutrient whose concentration in the water (for planted aquariums about 0.2 to 0.7 mg / l) by adding more fish food or sodium hydrogen phosphate ( Na 2 HPO 4 or NaH 2 PO 4 ) and also potassium dihydrogen phosphate (KH 2 PO 4 ) can be increased.
  • Potassium : from 0.5 to 30 mg / l


  • Iron : Aquarium plants can develop chlorosis (yellowish-white discoloration of young leaves) due to impaired chlorophyll formation with a lack of iron (less than 0.1 to 0.3 mg / l) as well as with a lack of nitrates. When fertilizing with iron supplements, a distinction must be made between chelated and non-chelated iron (e.g. in the form of iron citrate ) , particularly with regard to the dosage .
  • Copper ; both trace elements and (from 0.5, sometimes from 0.1 mg / l in aquarium water) plant toxins
  • Zinc : Plant nutrient that is contained in trace element fertilizers and should be present in the aquarium water in a concentration between 0.002 and 0.02 mg / l. From 0.05 mg / l, phytotoxic damage patterns similar to those caused by too much copper appear in many plants.

Economy, science, nature and animal protection

Origin of the organisms kept in the aquarium

Most of the freshwater fish regularly offered in pet shops come from offspring. It is estimated that there are 300 million ornamental fish that are raised for the aquarium trade every year.

The fish are mainly bred in Southeast Asia. Breeding stations are mainly in the area around Hong Kong , Singapore and Bangkok and to a lesser extent in Sri Lanka , Japan and Taiwan . There are also large ornamental fish farms in North and South America , in some South African countries as well as Israel and the Czech Republic . Breeding systems for seawater fish have been built especially since the mid-1990s.

For transport by air to the importing countries, the fish are usually packed in bags, one third of which is filled with water and two thirds with air or oxygen. Air is used in species like labyrinth fish and armored catfish because they also breathe atmospheric air. Pure oxygen would be deadly to them. Occasionally, an anesthetic is added to the water so that the metabolism of the fish is not too high and the water is not too polluted. Ornamental fish exporters also fast their fish for a few days before they are transported in order to keep water pollution low. The bags are then packed in polystyrene boxes and flown to their destinations. One of the large cargo airports where many ornamental fish arrive is Frankfurt Airport . Importers are usually wholesalers who initially keep the fish in quarantine tanks and usually only sell them after seven to 14 days.

Piranha caught in the wild

Furthermore, fish, plants and invertebrates are still being taken from the wild around the world for animal and plant export. Especially in countries with a low per capita income, this can represent a significant source of income for parts of the population in rural regions. Above all, fish that are not or only very difficult to breed are regularly imported. In addition, there is great demand for new aquarium items. The number of wild catches is estimated at 30 million per year.

The negative effects of collecting fish and plants are repeatedly and critically discussed. Criticisms cited include that when reef fish are caught in the wild, coral reefs are destroyed, many other animal species are removed as bycatch and species stocks are so heavily plundered that populations in the original range collapse. Group expeditions are lengthy, costly, and not always successful. The transport to the export centers can be very stressful for the animals. Many aquarists therefore only keep fish from offspring. Among US aquarists who specialized in saltwater aquariums, two-thirds of those questioned in a 1997 survey said that they would rather buy fish from offspring than wild-caught fish. 80 percent of those surveyed also stated that only those fish should be placed on the market that either ensure the continued existence of the species on site through catch quotas or that come directly from bred fish.

Animal welfare aspects

When operating the aquarium hobby (whether professionally such as in zoos, breeding establishments or in science or amateurish as a leisure activity), it must be noted that fish are living beings to whose keeping animal welfare law applies.

Keeping fish species in the aquarium as appropriate to the species as possible requires, like any keeping of living things, sufficient knowledge. Many aquarists invest a lot of time and money to provide good conditions for their fish or invertebrates. A number of aquarists also deliberately keep only those animals that can be bred and sometimes make great efforts to breed rarer fish species.

If insufficient knowledge is available, conditions can very quickly arise in an aquarium that can be viewed as cruelty to animals . Typical holding errors are:

  • too many fish and invertebrates. There are different rules of thumb for calculating the maximum stock size in the aquarium. As a guide, two liters of water are required in the aquarium for every centimeter of fish. (refers to the length of the adult animals)
  • the socialization of animal species that are incompatible with one another,
  • keeping animal species at water values ​​that are outside the spectrum where they are comfortable. Overfeeding can also contribute to the fact that water values ​​in the aquarium deteriorate and exceed a level that the fish can tolerate. Partial water changes that have not been carried out also usually lead to poor water values ​​(see backwater aquariums, however ).
  • the individual keeping of schooling fish
  • Keeping fish and invertebrates with territorial behavior in groups in tanks that are not large enough so that the animals behave very aggressively towards one another.
  • keeping fish in tanks that are not the size of the fish.
The silverfin leaf is often offered as a freshwater fish, but needs brackish water for its well-being

In the best case scenario, the fish react to these holding errors with delayed growth and reduced color. The fish perish more frequently, however, and death can take several months.

The quality of advice in specialist pet shops is highly dependent on the individual and ranges from a high level of professional competence to pure sales behavior. For some species, cultivated forms are offered which, from the point of view of a very large number of aquarists, represent excruciating breeding . These are, for example, goldfish with telescopically enlarged eyes or fins that are so enlarged that the animals can no longer behave appropriately. Species are also regularly offered that have very special holding requirements that very few aquarists can meet. For example, the silver fin leaf is regularly offered as freshwater fish, even though the fish needs a 1,400 liter aquarium with brackish water conditions when fully grown.

Breeding and maintenance breeding

The reproduction of their fish is of great interest to many aquarists. A spawning grid is used for fish that are not viviparous, especially open and ground spawners in the aquarium .

A number of fish species, invertebrates and aquatic plants are threatened with extinction or are considered to be extinct in the wild. Some tropical organisms have only very small areas of distribution. The South American Villavicencio dwarf cichlid has only been found in a few bodies of water near the Colombian city ​​of Villavicencio at the foot of the Andes and is threatened by biotope destruction . Endler's Guppy from the family of livebearing carp comes from a single freshwater lagoon in the northeast of Venezuela . It is considered extinct in the wild; as an aquarium fish, however, it is bred by both private individuals and public zoos such as the Cologne Zoo . This also applies to a number of other species. In its April / May 2006 issue, for example, the specialist journal Aquarium Live published a call from Peter Finke to participate in the conservation breeding of the Parosphromenus genus . These fish are among the most endangered labyrinth fish as their habitat is threatened by forest deforestation. The fish that live in the very acidic, almost mineral-free jungle streams of Southeast Asia are, however, very demanding in their keeping and are extremely rarely offered in specialist pet shops. However, there is a working group that has set itself the goal of stopping the extinction of this species of fish, at least in aquariums.

However, maintenance breeding is not easy to do. Fish bred in captivity can very quickly differ significantly in body shape and color from their fellow species living in the wild.

Science and aquaristics

Organisms kept in aquariums have repeatedly played a role in the natural sciences . This applies from Priestley's oxygen research using aquatic plants in the 18th century, to Konrad Lorenz's observations on territorial behavior using the example of sticklebacks in the early 20th century, to studies on the effects of pollutants dissolved in water today. The aquarium hobby also leads to the introduction of animal and plant species that have not yet been scientifically described. For some fish families in which the number of newly discovered species exceeds the speed with which they are classified, aquarists make do with code systems. For example, armor catfish that have not yet been classified are designated with L numbers . The repercussions of the commercial interest associated with the aquarium hobby on research can also be seen in an entirely different family: A few years ago, scientific research on freshwater shrimp was still focused on rock shrimp bred for human consumption in shrimp farms . Only since there has been a demand for species that can be kept in aquariums has research here expanded to include numerous other shrimp species.

Aquaristics as an economic factor

According to the Central Association of German Zoological Companies, 4 percent of German households had 1.9 million aquariums in 2019. The turnover for ornamental fish was 182 million euros , that of ornamental fish feed was 53 million euros.

Public show aquariums

Many zoos also have aquariums on their premises, such as the aquarium in the Berlin Zoological Garden , which has one of the oldest aquariums in Germany. The Aquazoo Düsseldorf , which is also a natural history museum, endeavors in its exhibition to make the adaptation of animals to their habitat clear. The collection is structured according to pedagogical aspects.

The numerous public show aquariums also include the German Marine Museum in Stralsund , the Ozeaneum Stralsund and the sea water aquarium in Wilhelmshaven . Further examples are the Oceanário de Lisboa in Lisbon , which was built on the occasion of the 1998 World Exhibition and is considered the second largest saltwater aquarium in the world, or the Oceanium , which opened in 2001 in the Rotterdam Zoo, Diergaarde Blijdorp .

On March 29, 2014 the largest aquarium in the world with a total volume of 48,750 m³, the Chimelong Ocean Kingdom , was opened. It is located on the Chinese island of Hengqin immediately west of Macau and 70 km southwest of Hong Kong in Guangdong Province . It contains 19 pools, was built at a cost of 1.5 billion euros and sets 5 world records: Largest acrylic glass pane (W × H 39.6 m × 8.3 m) as the largest aquarium pane, largest aquarium underwater dome, largest single tank.

The world's largest aquarium as of 2008, the Georgia Aquarium , is located in Atlanta , USA. The basins hold more than 30 million liters of water. Over 500 different species, a total of around 120,000 sea creatures, find space in this artificial reef. The main attraction are two whale sharks . These aquariums are often criticized for keeping such marine animals. The American Sea World chain with its dolphin and orca shows is particularly often criticized because it is doubted that such large marine animals can be kept in a species-appropriate manner. The also commercial British chain Sea Life Center pursued a different concept, at least in Germany, and worked with Greenpeace until 2006 . Greenpeace used the space for its own exhibitions. The Sea Life Center did not show any deep sea sharks, tropical fish species or threatened species. However, this obligation also prevented the Sea Life Centers from participating in conservation breeding.

Show aquariums on a smaller scale are also operated by some aquarium associations, which in Germany are predominantly part of the Association of German Associations for Aquarium and Terrarium Studies e. V. are organized. Other European associations have mostly come together in the European Aquarium and Terrarium Association.


History of the aquarium

  • Bernd Brunner: How the sea came home - the invention of the aquarium. Transit Verlag, Berlin 2003. (Revised and expanded edition Verlag Klaus Wagenbach. Berlin 2011.)
Bernd Brunner: The Ocean at Home - An Illustrated History of the Aquarium. Princeton Architectural Press, New York 2005. (Revised and expanded edition of Reaction Books. London 2011.)
  • Jörg Scheller : "Appetite for the Magnificent. An essayistic dive into the shallows of the aquarium using the example of Philip Henry Gosses". In: ders., David & Tania Willen, Appetite for the Magnificent. From aquariums . Edition Patrick Frey, Zurich 2017. (English edition: Appetite for the Magnificent. On Aquaria , Edition Patrick Frey, Zurich 2017; republication of the German text online on, December 3, 2018).
  • Mareike Vennen: The Aquarium: Practices, Techniques and Media of Knowledge Production (1840–1910) , Wallstein 2018 (received the Opus Primum sponsorship award )

Set up aquariums

Living things in the aquarium


  • Hans Frey: The aquarium from A to Z. 1st edition. 1957. (14th edition. Melsungen / Basel / Vienna 1976, ISBN 3-7888-0013-5 )
  • Claus Schaefer, Torsten Schröer (ed.): The large lexicon of aquaristics. Eugen Ulmer, Stuttgart 2004, ISBN 3-8001-7497-9 .
  • Daniel Knop: Lexicon of marine aquaristics . Natur und Tier-Verlag, Münster 2013, ISBN 978-3-86659-213-1

Trade journals

  • DATZ - the aquarium magazine . Nature and animals, Münster. ISSN  0723-4066 (electrical resource 2003 ff.)
  • Amazonas - freshwater aquarium specialist magazine. Nature and animals, Münster 1.2005.1ff. ISSN  1861-2202
  • Aquaristic trade magazine . Tetra, Berlin. ISSN  1437-4854
  • Aquaristics - Current Freshwater Practice . Dähne, Ettlingen. ISSN  0947-6512
  • VDA-aktuell - Association magazine of the VDA . VDA, Sparneck, ISSN  1863-4648
  • Aqua Terra Austria - magazine of the Austrian Association for Vivaristics and Ecology

Web links

Wiktionary: Aquarium  - explanations of meanings, word origins, synonyms, translations
Commons : Aquarium  - album with pictures, videos and audio files
Wikisource: Aquarium  - Sources and full texts

Individual evidence

  1. ^ Karl Ernst Georges : Comprehensive Latin-German concise dictionary. 8th, improved and increased edition, Hahnsche Buchhandlung, Hanover 1913–1918. 1918, Retrieved November 6, 2017 .
  2. a b Elena Nikulina, Ulrich Schmölcke: Fish farming in ancient Rome and its change in reputation in the light of the political situation . In: Writings of the natural science association for Schleswig-Holstein . tape 70 , December 2008, p. 36–55 ( [PDF; 1000 kB ; accessed on November 10, 2010]).
  3. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 72 f.
  4. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 100-105.
  5. ^ Hanns-Jürgen Krause: Aquarientechnik, Handbuch. 4th edition. Verlag Bede, 1999, ISBN 3-927997-10-2 .
  6. Martin Sander: Aquarium technology in fresh and sea water . Verlag Eugen Ulmer, 1998, ISBN 3-8001-7341-7 .
  7. Claus Schaefer, Andreas Raschke: Pocket atlas aquarium technology. Technology, furnishings, care . Verlag Eugen Ulmer, 2005, ISBN 3-8001-4675-4 .
  8. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 72 f.
  9. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 73 f.
  10. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 75-77.
  11. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 14.
  12. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 14.
  13. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 61 and 75 f.
  14. foreground plants (selected): needle ledges , dwarf leaf peer , dwarf sword plant , Bolivian sword plant , horizontal sword plant .
  15. ↑ Solitary plants (selection): Bleher's sword plant , Heart-leaved sword plant , Grisebach's sword plant , Horizontal sword plant , Wavy-leaved sword plant , Osiris sword plant , Rispige sword plant .
  16. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 66.
  17. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 66-68.
  18. Aquarium plants with higher maintenance requirements (selection): American pennywort , needle ledges , some water ears , water goblets of the Cryptocoryne cordata group, the sword plant Echinodorus gabrielii Rataj , the pipe root plant Tonina fluviatilis Aubl. , some Nesaea species ( loosestrife with low nitrate tolerance), especially Nesaea pedicellata , the rush Juncus repens Michx. .
  19. Aquarium plants with lower maintenance requirements (selection): Small and large fat leaf , dense leaf waterweed , some water friends , some sword plants, flooding arrow weed , Java fern , wavy water ear , false water friend .
  20. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 76-84.
  21. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 75-78.
  22. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. Tetra-Verlag, Berlin-Velten 2009, ISBN 978-3-89745-190-2 , p. 85 f.
  23. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 85.
  24. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 86.
  25. Christel Kasselmann: aquarium plants. 2nd, revised and expanded edition. Ulmer, Stuttgart (Hohenheim) 1999, p. 60.
  26. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 19-24.
  27. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 19 f.
  28. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 24 f.
  29. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 60-62.
  30. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 60–62 and 91.
  31. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 66 and 90.
  32. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 63-65.
  33. Phosphate, nitrate and potassium in the aquarium (PDF)
  34. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 62 f.
  35. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 56–60 and 91.
  36. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, pp. 56 and 91 f.
  37. ^ Hans-Georg Kramer: Plant aquaristics á la Kramer. 2009, p. 91 f.
  38. Animal Welfare Act .
  39. ZZF: ZZF: sales data of the pet industry. Retrieved June 11, 2020 .
  40. For the fish: Largest aquarium in the world. In: , print edition of June 7, 2014, p. 8 f.
  41. Kevin Lynch: China's Hengqin Ocean Kingdom confirmed as world's largest aquarium as attraction sets five world records. In: , March 31, 2014, accessed June 7, 2014.
  42. ^ European Aquarium and Terrarium Association
  43. -joerg-scheller
  44. Thomas Steinfeld : Review
This article was added to the list of excellent articles on April 30, 2006 in this version .