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Source of Phosphate?

I recently paid $25.55 for 500 g. of potassium phosphate monobasic, KH2PO4,
from The Science Alliance -- enough, I imagine, for several lifetimes.
Fortunately, I was able to sell half of it to another aquarist.  And then,
in the drug store the other day, I stumbled on another possible source of
phosphate, which you may want to consider.

It's a mix of NaH2PO4 and Na2HPO4, dissolved in distilled water.  It comes
in a plastic squeeze bottle with a dropper and plastic cover.

The active ingredients are 19 g. of monobasic sodium phophate and 7 g. of
dibasic sodim phosphate, dissolved in 133 ml water.  According to my
calculations, this would provide 150 mg/ml PO4.  So, in a 100 liter tank,
one ml would add 1.5 mg/l PO4.  If that's too much, the bottle has a
dropper, and on the basis of about 20 drops/ml, you could use about 7 drops
to add 0.5 mg/l to the same size tank.

My first concern was whether the sodium ions might be a problem.  But I
calculate the solution contains only 45 mg/ml Na and would add only 0.45
mg/l Na to a 100 liter tank.  Compare that with a therapeutic dose of
aquarium salt (my box says to add 1 Tb per 18.9 l,)  That amounts to 400
mg/l Na!  So I wouldn't worry about 0.45.

My only other concern was that the label says the solution contains an
undisclosed amount of methylparaben.  As best I can find out, that's a
preservative, also used in foods and beverages.  It doesn't sound too lethal
to me.

The best part of this is that these bottles are widely available for about a
dollar apiece.  Just look on the shelves for a disposable enema.

John T. Fitch
E-mail: jtfitch at spamcop_net
Web Site: www.fitchfamily.com/aquarium.html