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[piatotsini]

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[Themuleous]

If Im not mistaken valls can use carbonate as a source of Carbon instead of CO2 and that can leave a white power on the leaves.

 

[zig]

Biogenic decalcification

Never witnessed it myself only read about it, it means you have a CO2 deficiency and classically it will appear as deposits on Vallisneria.

Some info here

When there is a carbon dioxide deficiencey in the water, plants can derive CO2 from the hardening constituents of the carbonate hardness. First they split the hydrogen carbonates into CO2 and carbonates. This causes the pH to rise about one step and the largely insoluable carbonates precipitate and form rough deposits on the leaves and substrate. Some plants such as Vallisneria can even destroy the carbonates and obtain CO2 from them. This raises the pH again by another step. Biogenic decalcification thus causes the water to be 10 to 100 times more alkaline than it was previous. In the dark, the process reverses and the pH drops considerably. Thus these continous large pH swings can pose a significant risk to the well being of fish and animals. The solution is to add enough CO2 to the water and have a significant carbonate level to act as a buffer.

 

[zig]

Its basically stripping the KH out of the water, so if your KH is low to begin with this can cause problems outlined above with Ph swings.