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Re: pH VS ammonia
Charles n Sue Harrison wrote:
>
> As long as the pH of the water is below 8.5 the effect of ammonia in
> not a problem. as a matter of fact, the ammonia if present would
> remain as its salt even if the water were boiled away to almost
> dryness.
It is tough to argue such points with a chemist, but I must respectfully
disagree, both from what I know through reading and have directly
experienced.
Yes, the ratio of ammonium to ammonia is theoretically constant at all
concentrations if it is evaporated away without heat. It varies most
strongly with pH and to a lesser extent with temperature. In your specific
example, the ammonia will quickly boil off as gas, and leave *only* the
harmless ammonium ions. That's not what happens in an aquarium, though.
There, the tendency is for the fish to produce more all the time.
Ammonium and ammonia have an equilibrium relationship that varies with pH
and temperature. The percentage in the dissolved but not ionized ammonia
(NH3) form, at 20C, jumps from 0.5% at pH=7 to 13.7% at pH=8.5. [Spotte,
1970, p104] That means that 86.3% remained as the ion (NH4+) form, so you
are correct, in that *most* is still harmless ammonium.
However, the basic *toxic* material is over 27 times higher at a pH of 8.5,
until we do something to remove it, such as long-term aeration,
biofiltering, plant feeding, etc. In any compromise between food and poison,
the poison will inevitably win.
The overall toxicity of ammonia can be altered by lots of other factors.
Supersaturation with oxygen seems to reduce damage, somewhat. Nevertheless,
ammonia is lethal at levels well below what the average test kit can
indicate, and the stunting and subtle disease-inducing damage can be severe
at far, far lower levels.
Spotte goes on to point out that Burrows (1964) found clubbing (hyperplasia)
and permanent damage to gill filaments of salmon fingerlings at levels of
ammonia of 0.006-0.008 ppm (0.3 ppm total ammonium/ammonia). [This was at a
pH of only 7.8, BTW.] The younger fish never recovered, when returned to
clean water. They were stunted, permanently. Older fish did recover after 3
weeks in new water. Results on minnows and other fish were much the same, so
the damage was deemed to not be species specific. Burrows suggested that
exposure to ammonia at such levels also was the precursor of bacterial gill
diseases.
Betta owners often do frequent, 100% water changes. In recent years,
literally thousands of Bettas have been killed when the dechlors based on
thiosulfate were used but the city water had changed to chloramine. It was
more obvious with them, because the ammonia was so much higher level with
100% water changes. It was quite lethal in water of pH only in the mid 7s.
It made real believers out of a lot of Betta folks, particularly when that
year's co-Grand Champions were *both* completely wiped out, by ammonia, at
opposite ends of the country!
In killies, I have seen numerous examples of sickly fish and sudden breeding
failure due to the same problem. Incredibly tiny amounts of ammonia can
sterilize wild rainforest killies almost completely. If exposure is low
enough, they sometimes recover fertility. We nearly lost one of the
still-unidentified TDK 97 Gabon species through this (or a related)
mechanism. Luckily, they started producing viable eggs again after months of
recovery.
While Spotte and Burrows seem to think the effects of ammonia are not
species-specific, like some organic metabolites, I have a feeling that some
of the harder-water species are a bit more rugged and tolerant than fish
that really need soft acid water, wild fish, or fish with very high
metabolic rates. Maybe the damage is comparable, but they just show the
results differently.
Anyway, Charles, until you have been there and experienced it for yourself,
I suggest that advising folks that ammonia isn't a problem at pH=8.5 is not
a really good idea. You don't have the same fish or local circumstances that
they do, and the overwhelming evidence is that control of ammonia is the
single most important water factor in most artificial maintenance
situations.
You can add ammonia-containing fertilizers if you like. I have killed wild
Amazonian fish by stupidly using a fertilizer that I didn't realize
contained ammonium nitrate, in a planted tank, and it was in really tiny
amounts, too.
That's my $0.02 (again) on the subject.
Wright
--
Wright Huntley, Fremont CA, USA, 510 494-8679 wright at killi dot net
http://www.atchison.com/Killifish/BAKA-WCW-10.html
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