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Re: Dosing NH4 or NO3?

> Date: Sun, 8 Apr 2001 10:26:22 +0200
> From: "Klaus Haber" <kh3515 at bingo-ev_de>
> Subject: Dosing NH4 or NO3?
> Hello,
> in the moment is running a discussion concerning dosing PO4 and NO3 (if
> necessary). My tank has a deficit of NO3 and PO4 too, due to lot of plants,
> bright light and a moderate fishload. So I decided to dose PO4 and NH4
> additionally. I use a solution of (NH4)2HPO4, Ammoniumhydrogenphosphat.
> But my question is this: If there is a nitrogen deficit, is it better to
> dose NH4 than NO3 or not? I heard, for plants it is easier to utilize NH4
> because they need less energy to get to Nitrogen as it is with NO3. Is this
> true? If "Yes", why do the most folks dose NO3 and not NH4?
> Thanks for reply,
> Klaus.

That's an easy one Klaus. 

Ammonium is easier for the plants, but can harm, stunt and even kill fish if
the pH gets a bit high at any time. The plants have to work harder to
utilize nitrates, but those are harmless at concentrations below 100 ppm or
so, at any pH.

The equilibrium between ionized ammonium (harmless to fish) and dissolved
gaseous ammonia (highly toxic to fish) goes from all ammonium at a pH in the
mid 6s, to as much as 13% ammonia at pH=8 (as I recall). Anyway, the
toxicity is about 50 times higher at pH of 9 than it is at 7.

As little as 0.01 ppm of ammonia has been shown to cause gill damage and
stunting in baby fish, so it just isn't worth the risk unless you know for
sure your pH will stay at or below 7 (or you have a fishless tank).


Wright Huntley, Fremont CA, USA, 510 494-8679  wright at killi dot net


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