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Re: biogenic decalcification

Laurel Merrel wrote:
> 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?

Probably not, unless you provide some fairly specific conditions.  If
you have biogenic decalcification going on both the alkalinity and Gh
should drop together when the the tank is lit and may rebound slowly in
the dark.  The pH will be very high--high 8's up to 10 or so -- while
the tank is lit.

For all this to happen you need an absence of CO2 plus bright light --
probably sunlight.  I used to see biogenic decalcification when I had
tanks lightly stocked with fish in a south facing window where they
received 6 hours/day of direct sunlight.  In my case biogenic
decalcification didn't cause much of a drop in alkalinity or GH because
the calcium content in my water is too low to precipitate much calcium

Nitrification lowers alkalinity.  Other sorts of acids -- particularly
organic acids that might be released by driftwood or peat -- can also
low alkalinity.

> 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?

You're probably better off adding calcium carbonate.  It will raise both
alkalinity and GH.

Roger Miller