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CO2 and KH

>I have a digital model that I can use
to solve
>chemical problems under fairly complex
conditions like in aquariums. I ran
>some tests with the model and it
appears that the increment in dissolved
>CO2 that you get from increasing the
bubble rate should be the same
>regardless of what the starting pH is

Does this mean that you agree that the
addition of baking soda to raise the kH
should do nothing to prevent pH swings
caused by CO2 injection?

>The model did confirm the pattern
(observable on the CO2-KH-pH charts)
>that the change in pH that comes from
an increase in CO2 is larger at high
>pH than it is at low pH; the lower the
pH is to start with, the more
>difficult it is to lower the pH.

I am afraid I do not understand this. I
thought you just said that the change
would be the same regardless of the
initial pH. Of course once the pH has
been lowered using CO2 an additional
change of the same amount will require a
much greater amount of CO2.

In the end though this does not explain
why the pH in Mr. Moncurs tank does not
drop significantly when he adds CO2.
Surely, one bubble per second in that
size tank with low suface turbulence
should be enough to make a pH change
greater than .2. I have also heard many
other people state that it is more
difficult to lower the pH of hard water
than soft water using CO2. Is there
typically some other ingredient in hard
water that prevents CO2 injection from
lowering the pH?