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Re: Acidic kitty litter


On Wed, 12 Jan 2000, Sylvia wrote:

> I assume this is how peat both softens and acidifies the water as well? I
> realized that it releases humic acid into the water, lowering pH,  but
> wondered about its *softening* effect.

The effects from peat (either softening or acidifying) are variable, just
as are the exchange capacity and pH of clays.  To get a softening or
acidifying effect from peat you need to shop around for a peat with the
right properties.  Peats aren't all created equally, and some may be
treated (with lime, for instance) to enhance or suppress different
characteristics.

The softening effect of peat is due to the same mechanism that allows
zeolites and clays to soften water.  Peat has an ion exchange capacity.
If you are using peat with a low ion exchange capacity, or one that is
charged with calcium or magnesium then the peat will have little or no
softening effect in your water.  This is also true of clays and zeolites.

Unlike clays and zeolites, the ion exchange capacity of soil humus (and
I think this can be extended to include peat) depends on pH.  The higher
the pH, the higher the exchange capacity.

The acidifying effect of peat and acidic clays are different.  Peat
contains complex, weak and poorly soluble organic acids.  The acids can
act as a buffer by releasing hydrogen ion when the pH increases and
combining with hydrogen ion when the pH decreases.

Acidic clays aren't actually acids and they don't release hydrogen ions in
response to changes in pH.  Rather, the hydrogen ions are adsorbed on the
clays and they're released when there are other ions present that can
replace the hydrogen on the clay particles.  There is little or no
buffering effect.

I don't know of any established risk to your aquarium plants caused by low
pH substrates.  I think this is because of the difficulty of isolating
effects in an aquarium and not because there is no effect.  I figure that
aquarium plants will be just as sensitive to low pH substrates as are
terrestrial plants.  Soil acidity is a feature that some plants are
adapted to, and some are not.  Plants that aren't adapted to acidic soils
grow very poorly in them.  The same can be said for plants and alkaline
soils.  Probably some of our aquarium plants are well-adapted to an acidic
substrate and some will not grow well in an acidic substrate.


Roger Miller

P.S.  Seeing Sylvia's return address reminds me, I owe apologies to Sylvia
and a few others of you on AOL who sent me email and never got a response.
Until recently I had a filter on my email inbox that trashed anything
coming from an AOL address.  That's because at one time I was getting
nothing but junk mail through AOL.  I recently found some letters from
Sylvia and a few other APDers that were routed into a junk mail box.  I
also noticed that I'm getting a lot less junk through AOL, so I changed
the filter on my inbox to allow mail from AOL.