Re: Biogenic decalcification

If your pH rises during the day and falls at night, then the rate of 
uptake of CO2 into the plant is greater than the influx of CO2 into the 
tank. This creates a CO2 deficit during the day. Biogenic decalcification 
will ONLY occur if your plants are able to 'use' bicarbonate. In the 
course of bicarbonate uptake, hydroxyl ions are released by the plant ... 
these ions react to form calcium carbonate which then precipitates out of 
sulution, hence the decalcification. Depending on your CO2 deficit, the 
pH could rise as high as 9 or even higher ( only if your plants use 
bicarbonate ... in fact this is how early experimenters determined which 
plants could use bicarbonate). If your plants cant use bicarbonate the pH 
will still rise but not as high and the Ps rate of these plants will be 
significantly reduced when the pH does rise.

The solution is to increase the influx of 
CO2 into your tank. In a recent rant I recommended increasing the flow 
rate of water across the top of the tank, either by powerheads or 
aeration. Alternatively, you could add ... dare I say it ... CO2.