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Re: Aquatic Plants Digest V3 #204
Roger Miller wrote:
>Under favorable conditions, hydroxylapatite is essentially insoluble.
>I turned around a calculation (perhaps a little too quickly?) and
>found that at pH 8 with 4 degrees of general hardness (all as
>calcium) hydroxylapatite solubility would allow something like 0.6
>part per trillion (not a typo) of HPO4 in solution. With 8 degrees
>of general hardess this drops to about 0.2 parts per trillion.
>All that aside, I wasn't aware that hydroxylapatite played a role in
>water treatment. Someone might set me straight on that. <snip>
I got it from:
Manahan, S. 1979. Environmental Chemistry. Willard Grant Press,
Chapter 8 is entitled "Water treatment", and phosphorus removal is
covered in section 8.18.
My tap water has virtually no phosphate, but ample calcium (18 ppm Ca
and 6 GH) and high pH (9.8). I suspect our treatment plant is
removing phosphate (and lowering hardness), but I do not know how they
Your calculations indicate that in the presence of Ca, there is very
little soluble PO4. Many people report phosphate levels of >1 ppm in
their tanks. Does this mean they have very little Ca? Or is the
phosphorus in another form (organic?) that will not precipitate?