As chemist, I'm a fair electrical engineer, but... (^_^)
It usually isn't actual direct chemical burns from acids or alkalis, IMO.
My observations are that the pH problems are a cause of secondary effects.
Most of the damage from wildly off pH are ammonia or nitrite problems.
More ammonium converts to ammonia at high pH and sometimes that suddenly
becomes quite deadly. About 50 times more of it is in ammonia form at pH 9
than it would be at 7. A reverse effect happens when nitrites are present,
for low pH is the more dangerous condition. IMHO, about 98% of pH shock
problems are from one of those or plain old osmicity shock due to tds change
being too fast (particularly when the change is downward, and gill cells are
burst).
I once killed a tank of killifish by letting pH get too low, and dissolving
some lead plant anchors. They were apparently done in by lead poisoning --
again a secondary effect. Lead is pretty inert above pH 6 or 7, and totally
so above about 8.
I have frequently exposed fish to pH changes of 2-3 whole points (e.g., from
6.0 to 8.0) with no obvious effects if a) the water was really clean and b)
the tds of the water was constant. This leads me to believe that fish don't
care a lot about pH, itself, but may have strong reaction (like not
breeding) to secondary things that are linked to pH.
pH kits are just way easier to sell and use than subtle ionic balance tests
of a host of obscure organic compounds. :-)
Wright
-- Wright Huntley, Fremont CA, USA, 510 494-8679 huntleyone at home dot com"DEMOCRACY" is two wolves and a lamb voting on lunch. "LIBERTY" is a well-armed lamb denying enforcement of the vote. *** http://www.self-gov.org/index.html ***