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Re: Phosphates, which one?

Luca Specchio wrote:

> Phosphate- limited tank is almost a Bible, but which phosphate ww would
> look for to understand that a tank is limited or not, or - maybe - too much
> limited???
> I know at least 3 types of P:
> ortho-phosphates
> poli-phosphates
> organic-phosphates

You can probably assume that any soluble form of phosphorus will be
available to plants and algae.  So try using the sum.

The phosphate test kits I've seen are variants on the molybdate test for
dissolved P.  That test generally regarded as a test for
orthophosphates, but it's non-specific enough that some literature cites
those results just as "molybdate-reactive phosphorus" or MRP.

I have seen evidence in the literature that algae can use organic
phosphates directly.  I don't know if plants can or not, but I'm pretty
sure that organic phosphorus can be cycled into orthophosphates which
*are* available to plants. I'm also not sure about polyphosphates.  I
think those are mostly synthetic compounds and I expect they break down
to something that will be biologically available.

Roger Miller