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CO2 and KH
Earlier in this digest I opined (in response to a question by Michael
Moncur) that if you increased the CO2 bubble rate into a tank with high pH
you would see a smaller increase in dissolved CO2 then you would if you
made the same increase in a tank with a lower pH.
Regardless of how reasonable that seemed to me earlier today, it now
appears to be wrong. 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. This assumed that *all* of the
added CO2 was dissolved and none was lost directly to the water surface.
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.