[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Ca as PO4 remover?
Those familiar with water treatment methods know that:
5 Ca + 3 HPO4 + H2O --> Ca5OH(PO4)3 + 4 H
Hydroxyapatite (Ca5OH(PO4)3) precipitates out. The addition of
calcium is a good way of removing phosphate (conversely, the addition
of phosphate is a good way of removing calcium). As long as calcium
is in excess, the amount of PO4 remaining in solution is dependent on
the solubility of hydroxyapatite.
Typically, PO4 in our aquaria is higher than our tap water, largely
due to the addition of fish food. This implies that those of us with
ample Ca may have a natural cap on the amount of PO4 in our water (as
long as we do regular water changes), while those with soft water may
benefit from the addition of Ca. Another benefit is
sedimentation--phosphate would drop out of the water column and into
the substrate, where it could become available to rooted plants.
Does anyone know the solubility of hydroxyapatite, and how
pH-sensitive is this reaction? If it only occurs at high pH, then it
isn't really feasible for aquarium use. Would the addition of Ca be
as effective as a phosphate-absorbing resin?