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# re: KH, pH, CO2 table ...

> pH as a function of CO2 concentration and KH value:
> 7.58+@LOG(KH)-@LOG(CO2)
>
> CO2 concentraction at a given pH and KH
> 10^(7.58-pH+@LOG(KH))
I plugged the second of these formulae into my trusty spreadsheet, and was
surprised to see that it gave results that vary from the tables on the
Krib. Those two tables agree fairly closely with each other. The formula
above yields values that are consistently slightly to somewhat higher.
For example, at ph=6.6, KH=10dKH, the table yields 74-76ppm CO2, but the
formula yields 95-96ppm CO2. (Values past the cusp of the exponential curve
are off more than values prior to the cusp, so even if the formula or the
tables are wrong, the error would be much less for CO2 values safe for
fish).
Does anyone know the original source of those tables on the Krib? Were they
derived empirically, or from the equations governing equilibria? I am
tempted to dust off my high school chemistry knowledge and a CRC handbook
and figure this out for myself, but I remember these weird
multiple-equilibrium systems being taxing.
-matt
on vacation in chilly Seattle