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Re: PH Question

> Date: Sun, 24 Nov 2002 13:34:01 EST
> From: Billinet at aol_com
> Subject: PH Question
> Hello,
> It was recently posted that the fish and the plants didn't care what the pH 
> was.
> OK.
> But in a moderately well-planted tank (about 1.5 growing rooted plants per 
> gallon - a new ratio?) with a fish load of about one inch per gallon, 2 watts 
> per gallon of light, and no injected CO2, wouldn't the tank work better if 
> the pH was on the acid side?  I'm thinking that the ammonia - ammonium 
> conversion, which takes place in an acid environment, would make a 
> difference.  Right?

If the pH is below about 8, the amount of ammonia is usually pretty 
insignificant. It does not have to be acid to be mostly ammonium. Yes, it 
makes a difference, but the change is gradual and significant ammonia 
percentages don't grow until pH is up around 9 or above. Even then, as I 
recall, about 2/3 or more is still in the ammonium form, so the plants 
aren't starved. The fish may protest that their gills are burning, tho, if 
total ammonium/ammonia is too high (>0.25ppm or so) [IDK if the plants feel 
it the same.]

Modest water changes take care of that, usually.

> And in a related question, is the fact that nitrates often have to be 
> supplemented in a tank with growing plants due in part to the fact that 
> "nitrogen cycle" is bypassed in an acid environment, with the ammonia 
> converting to ammonium and being taken up directly by the plants rather than 
> being converted to nitrites and nitrates?  Would the answer be different in 
> an alkaline environment?

I doubt it. The reduction in the ammonium fraction isn't very significant 
until the pH gets really high (10+). Plants growing at a given rate need a 
given amount of N2, whether they get it from ammonium or from nitrates. 
Supplementing is because fish poop isn't adequate, and pH (below about 9) 
probably isn't too significant to the process.

At really high pH, enough ammonia fraction may be present to cause 
significant loss to the air as that ammonia is evaporated out of the tank. 
That's good for the fish, and one might even need increased nitrate 
supplementation to replace the loss.

If your tank has the usual carbonate/bicarbonate buffering (high 7s before 
CO2 is added) then the vast bulk is as ammonium and not ammonia, so one need 
not worry about it too much. There are other advantages to lower pH, such as 
reducing certain bacteria and making some materials more soluble, but the 
effect on ammonium/ammonia and the nitrogen cycle is probably pretty 
unimportant until pH is above about 8.5 or 9.


Wright Huntley -- 209 521-0557 -- 731 Loletta Ave, Modesto CA 95351

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