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RE: CO2 determination from charts

Colin Anderson was wondering about his CO2 levels, as determined by the
CO2-pH-KH charts, and from his posted numbers, it would appear that he has
very high levels of CO2 in his water.

> Date: Mon, 09 Nov 1998 08:27:47 PST
> From: "Colin Anderson" <colin_d_anderson at hotmail_com>
> Subject: pH 6.4 kH 7
>     test    tap       tank
>     gh      22        18     dH      Red Sea Labs kit
>     kh      7         7      dH      Aquarium Pharm. kit
>     pH      7.4       6.4            Wardley kit
> Thanks for the response Carlos, they've been pretty thin on this
> question.  I don't use any buffer up/down or sideways, also no peat,
> although I've considered it.
> What your telling me is that if my pH and kH are accurate, one of two
> things is happening.  First, I have 70ppm CO2, and all of my fish are on
> some sort of steroid and can live through this.  Or, Second, I've got
> some buffering which is not identified by these tests.

I'm not an expert on the equation used to derive the numbers in the chart,
but I do remember someone, I believe it was George Booth, stating that in
order to be able to effectively use the chart you not only had to stay away
from odd buffers (like peat or phosphate based buffers) but you also had to
know your pH and KH with a very high degree of accuracy and precision. I
believe that George uses either a LaMotte pH test kit or a calibrated pH
electrode to measure his tank's pH, both techniques I would guess are a lot
more accurate than any kit put out by Wardley (what is the scale definition
of the kit?). Similarly, how precise is the Aquarium Phar, KH kit? I have
one, and I wouldn't bet my CO2 concentration on it - the color comparison is
to a poorly printed piece of paper.

My point it that what appear to be minor errors in measuring pH and KH could
throw your CO2 reading way off - so far off that the result using the chart
cannot be trusted.

Why not just buy a LaMotte CO2 test kit and be done with it? They aren't
THAT expensive.

James Purchase
Toronto, Ontario
jpurch at interlog_com