Biogenic decalcification

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As Biogenic descaling (including bicarbonate assimilation ) refers to a process wherein the submerged aquatic plants and phytoplankton by their photosynthetic consumption of carbon dioxide , the balance of dissolved calcium bicarbonate and carbonic move so that for the crystallization and precipitation of calcium carbonate occurs.

Some of the algae and plant species can also cover their need for carbon dioxide from hydrogen carbonate . They initially get their carbon needs from free carbon dioxide, as they have to use less energy for this. Only when this carbon source is largely used up do they remove the carbon bound in the hydrogen carbonate and immediately release hydroxide ions .

Both when the carbon dioxide is withdrawn from the dissociation equilibrium and when hydrogen carbonate is used, the pH value increases with the result that the mass ratio between hydrogen carbonate and carbonate is shifted in favor of the carbonate. The concentrations of dissolved calcium and carbonate , multiplied by one another, exceed the solubility product of calcium carbonate, which consequently crystallizes and precipitates.

The process takes place regularly in lakes and ponds. The milky cloudiness of the water that is often observed in alpine lakes in summer is due to this. Biogenic decalcification is the order of the day in carp ponds and attempts are often made to compensate for it by applying lime. However, this measure is based on a misconception. Although the pH value is currently being lowered by secondary effects, the risk of a renewed pH increase even increases in the medium and long term.

Aquaristics

This effect of increasing the pH value through photosynthesis in the plants and through the loss of CO 2 through ventilation is also undesirable in the aquarium . If the pH value exceeds the tolerance range of the organisms cared for in the aquarium, this can damage both fish and other organisms. A dense planting of an aquarium, which thus ensures the oxygen requirement, always goes hand in hand with a high consumption of carbon dioxide if there is sufficient lighting. Further influencing factors are the nutrient content due to feeding, the fish stock, temperature, soil, water movement and the frequency of partial water changes . Experience has shown that small aquariums are more exposed to biogenic decalcification with a corresponding increase in pH than large ones. The carbon dioxide content of the water, which controls the pH value, can be checked with a CO 2 long-term test.

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literature

  • Kurt Bauer: On the importance of carbon dioxide in carp ponds. In: Austria's fishery. 44, 1991, ISSN  0029-9987 , pp. 49-64.
  • Hans-Georg Kramer: Plant aquaristics á la Kramer. Tetra-Verlag, Berlin-Velten 2009, ISBN 978-3-89745-190-2 , p. 66.