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Re: pH and ammonia, Who said ammonia anyway

> Date: Tue, 6 Oct 1998 08:38:16 +0600
> From: "Charles 'n Sue Harrison" <csharrison at primary_net>
> Subject: Re: pH and ammonia, Who said ammonia anyway
> This is Charles Harrison in St. Louis
> 	I would like to interject the relationship of ammonia in our fresh
> water systems is less than trivial. Ammonia does not exist at measurable
> amounts at pHs we consider safe for our fish.

Sorry, this happens not to be the case.

> 	Free measurable ammonia does not occur is water with a pH below 10.
> Do the calculations yourself. Just remember that the amount of cation
> charges and anion charges must balance, and ammonia in not ionized, it is a
> gas dissolved in water. This kind of talk sounds like some kind of Witch
> Craft, John.

Ammonia gas ionizes in water to produce NH4+ and OH-.  Ammonium ion (NH4+)
is much less toxic than NH3.  The ratio of NH4+/NH3 varies with pH.  At
pH 10 it's about equal, at pH 9 it's about 10 to 1, at pH 8 it's about 100
to 1 and at pH 7 it's about 1000 to 1.  So if your pH is always below 7,
it's generally not a problem unless the total concentration is really really
high.  However, if your pH is above neutral, or definitely basic as in a
rift lake, brackish or marine tank, even relatively low amounts can be a
problem because ammonia is so toxic.  pH can rise abruptly in soft water
in which a lot of photosynthesis is taking place, as CO2 and bicarbonate
are stripped from the solution by the algae or higher plants.