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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 Charles, but that is simply not true.
> 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.
Strong words, Charles. OK, try *this* witchcraft on for size.
Ammonia is in equilibrium with ammonium ions over a wide range of
conditions. The exact percentage of which is influenced slightly by
temperature, but dramatically by pH. The reduction of H+ ions at higher
pH is what does the trick. The ammonium *is* ionized but changes to
ammonia to balance charges, as you say. At pH=9, and 20C, about 36% of
the combination will be dissolved ammonia and the rest ammonium ions. By
pH=9.5, it is over 60% ammonia! The percentage of ammonia also
*increases* somewhat at the higher temperatures of typical tropical
Since less than 0.01 ppm of ammonia is measurably gill-damaging and even
potentially lethal to fish, to propagate any misinformation on this
subject is serious indeed, IMHO.
This phenomenon *is* susceptible to calculation, but you just may have
used the wrong formula. I've done it, and my calculations agree rather
nicely with the results in Spotte's _Fish and Invertebrate Culture_ ,
Wiley, 1970, p104.
In 1955, Downing and Merkins (*Ann. Appl. Biol.*, 43: 243-246) reported
that a reduction of pH from 9 to 8 resulted in a ten-fold reduction of
unionized Ammonia, (as reported in the above reference). To go from 9
down to 7 results in a whopping 70 times reduction, BTW!
As chloramine has replaced chlorine in urban water supplies, I,
personally, know a number of top fish breeders who were simply wiped out
by thinking sodium-thiosulfate-based dechlor products were still safe.
The high pH mandated by EPA (to limit lead and copper) combined with the
tiny release of ammonia from the chloramine was devastating. I even know
of one major fish show that had about 90% mortality, but the exact
numbers will never be known due to a successful cover up.
To any who doubt this, I suggest you read Chapter 7 of the Spotte
reference, re: "Toxic Metabolites." [This book is widely considered to
be *the* definitive text on "Water Management in Closed Systems", BTW.]
Wright Huntley, Fremont CA, USA, 510 494-8679 huntley1 at home dot com
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