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[APD] Re: Triple PO4

>From: "Thomas Barr" <tcbiii at earthlink_net>

>> Can P2O5 Triple Superphosphate (0-45-0) be used in place of KH2PO4?
>It's not that suitable.

I suppose that superphosphate [calcium phosphate {Ca(H2PO4)2}]  is not
suitable for water column application because it is extremely insoluble.
Folks have suggested pulverising, but this is very time consuming and
outcome is still unpredictable. Certainly, the small amount of Ca would not
noticeably change water hardness.

However, this got me to think about another way to dose phosphate. What
about Phosphate rock, or the mineral fluorapatite (Ca5(PO4)3F) which is
processed to become superphosphate.
Is it possible that someone can calculate the rate at which calcium
phosphate rock dissolves in aquarium water (for aquarium water temperature
and other relevant parameters), and then determine what amount of the rock
by surface area could be inserted into a tank to provide a SMALL but
CONTINUOUSLY provided amount of phosphate to feed the plants. The effects
of dissolved F and other contaminants would also need to be evaluated.
Maybe there is a nongranular form of superphoshate that could be fashioned.
Such an approach could further simplify the "Barr Method." 

[Roger, is Texas "Holy Rock" used by cichlidophiles a phosphate rock?  If
so, then there is lots of anecdotal evidence about its safety in aquariums]  

Another source of slow release phosphate, but only for soft water aquariums
might be uncrushed oyster shells for the filter box or measured (small)
amount of crushed shell.  This can also help with Ca depletion for soft
water situations. 
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