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Re: CO2 Measurements

On Wed, 1 Dec 1999, Aquatic Plants Digest wrote:

> In summary, conditions in the aquarium have been pretty stable for several
> months. I throw some peat in, and bang ! the pH drops and the kH doesn't
> change. So if I blindly apply the Ph/Kh/CO2 relationship, I would conclude
> that CO2 jumped from 40 ppm or so to well above 100 ppm. This obviously
> didn't happen, so I conclude then that peat throwed the Ph/Kh/CO2 relationship
> out of whack.

Peat changes the pH-KH-CO2 relationship *only* by adding alkalinity in the
form of weak, dissolved organic acids.

> I also could conclude that this particular peat wasn't good in
> decreasing alkalinity but very good in releasing acids, thus the observed
> pH drop which has no relationship at all with added CO2.

It appears that the peat probably destroyed a part of the alkalinity
provided by bicarbonate and added alkalinity in the form of inorganic
acids.  The amount of alkalinity added was close enough to the amount of
alkalinity lost that the net change in alkalinity wasn't measurable.

Roger Miller