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Re: Biogenic decalcification

> From: "L. Merrell" <merrell at u_washington.edu>
> Subject: biogenic decalcification?
> Hi. I posted a few days ago regarding my red melon sword with distorted
> leaves. I measured my various water parameters today and found that my dKH
> had dropped from a usual level of 4-5 down to 1 dKH. Could this be a case
> of biogenic decalcification? My other plants include: cypts, duck weed,
> azolla, glosso, rotala indica, bacopa carolinia, a red lotus and various
> swords.  Should I simply to a water change and watch the KH closely or do
> I need to dose with a carbonate source? Sodium bicarb or calcium
> carbonate?

	Biogenic decalcification is the removal by the plant of CO2 from
a solution of _calcium_ bicarbonate.  Calcium carbonate is precipitated,
and should be visible.  You didn't say what your GH is, but from the
calculations I have done on the chemical equilibria involved, I very
much doubt that you will get this with water that isn't pretty hard
(say GH10, KH10).  The pH will go very high, too - well over 8, probably
near 9.  It cannot occur with sodium bicarbonate.

Paul Sears        Ottawa, Canada