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RE CO2 causing a rinse in KH

Tomoko Schum wrote:

"What I reported originally was that KH suddenly shot up to6.0 while pH
stayed at 6.6.  This translates to the dissolved CO2 level of 45
milligrams/liter (and my fish was gasping for air.)  What is puzzling
to me is actually the sudden rise in dissolved CO2 level."

I don't blame my misunderstanding on your use of language.  I can blame
it on age, weariness, or a dozen other things that are mine and not

But anyway, now I think I understand what you meant.  And this
certainly is an interesting result -- a KH increase without adding more
CO2 yet the pH remains unchanged.  Did a turbulent tank condition that
was driving off dissolved CO2 cease at the same time the water supply
changed?  Has the water temperature decreased, thereby increasing the
amount of CO2 that can be adsorbed?  Have you measured any other water
conditions before and after the change in water supply?

Suppose those things haven't happened.  And let us assume that the KH
didn't, by itself, increase the miscibility of CO2 or the formation of
carbonic acid -- at least under normal circumstances it wouldn't.  If
another acid is present or forming, for other reasons, then the CO2
level could remain the same even though the KH is increased.  Could it
be that the new water supply has higher carbonates AND something else
(acidic or acid forming) that is holding the pH down, in effect, making
the KH:pH=>CO2 calculation misrepresentative?  If so, that something
else could be what's causing the gasping, not an increase in CO2.  An
independent test for CO2 levels would be nice to have.

I am glad you presented this interesting condition.  Maybe one of the
chemists out there can shed more light.

Scott H.

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