Re: PO4 and Fe

[Thomas Barr <tcbiii at earthlink_net>]

> Subject: KH2PO4 and Fe++ and Fe+++
> 
> I've just tried this:
> Mix a glass of water with TMG/micro achieving an orange/red color
> Pour in some KH2PO4.
> Notice the colorchange from orange/red to white/tranclucent.
> Wait and notice how the haze slowly settles on the bottom of the glass.
> 
> This can't be good.

Well not really.
I just tried adding to 500ml of DI water, 5mls of Flourish, 1/8th teaspoon
of KH2PO4 and got nothing, no precipitate.

I mixed the iron first, then the PO4. Zero, zip, nada.

So I tried the tap water in case the mix reacts with the KH/GH, again
nothing. So I tried it Plantex trace mix , again same result.

This is far more concentrated than any aquarium. I don't have any TMG
otherwise I'd test this.

How hard is your water's GH/KH?
 
> This would mean KH2PO4 is such a "hit" for some aquariums because
> the roots get their share of precipitated minerals and phosphorous?

No, the metabolic response from the plants happens too fast to be root
mediated. Also, the solids would need to get to the roots (not just the
surface mulm layer) and then be reduced, then transported to where the plant
needs it.

You can do a simple enough test to prove this notion in your own tank:
Add a solid powered form of PO4 to the roots(Use a pipette, syringe etc).
Time the response. Add KH2PO4 to the water column, time the response.
 
> This would also mean P-dosing should not be done in conjunction
> with Micros - for example with a syringe by the roots or by
> Jobe-sticks?
> Please elaborate.
> // Daniel.

I've not seen any precipitate although I've heard of it from others. Harder
waters seem to give a white precipitate with some trace mixes. Add the PO4
and the trace mix on opposite days if it makes you sleep better. I tried
that, but I don't find it makes anything grow better. I don't like having to
add things every day either or almost every day. To confusing, PITA etc.
Adding everything every 3 days to 2x a week is easier.

My notion is that it doesn't matter a whole lot. The PO4 and iron will be
used either way. 

Regards, 
Tom Barr