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Re: Cation Ratio's

On Wed, 9 Dec 1998, James Purchase wrote:

> Or does it really not matter if the ratio of the cations in our tanks and in
> a tropical stream is different, given sufficient Ca, Mg and K for plant
> growth?

Different streams have different water compositions, and one stream can
have different compositions at different times.  Changes are due to
changes in rainfall patterns, land use and any number of other causes both
completely natural and anthropogenic.  As a result, I doubt that most
variations in cation (or anion) ratios are of any significance to
plants.  The same can be said for variations in total dissolved solids
content (TDS), within reason.  Things won't grow well without some
dissolved solids, and most of our plants don't seem to do well in brackish
water, but there's a lot of variation in between where conditions are good
for plant growth.

There may be one problem with cation ratios that happens under extreme
conditions.  I have read that calcium deficiencies in terrestrial crops
can occur in high-sodium soils even when the calcium levels are up to what
would usually be sufficient for normal plant growth.

I have on-going problems with calcium deficiency symptoms in one of my
tanks.  My water is soft, but the calcium content isn't so low that it
should cause deficiency symptoms.  I've even added calcium to the tank
without relieving the symptoms.  My water has a very high proportion of
sodium - about 91% of the total cation equivalents are sodium and I
suspect that this is the cause of my calcium problems.

My water is naturally weird, but anyone who uses water from an
ion-exchange water softener and has total hardness of 1 or 2 degrees GH
will probably have water that is similarly dominated by sodium.  My
problems are in a high-input tank and appear mostly in Echinodorus and
vallisneria.  The same plants grown in the same tap water in other tanks
with lower light and less fertilizer don't show the symptoms (deformed new
growth, slow growth and under extreme conditions death).  Has anyone else
run into this problem?

Roger Miller