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Re: KH/pH/CO2 ???
> From: "Newcomb, Lew" <lew.newcomb at eds_com>
> Subject: kH/pH/CO2 ???
> I have made an odd observation. I've been examining the kH/pH/CO2 chart
> found on the SFBAAPS and other web sites, and I decided to check out where
> my tank falls on there. I have a Red Sea "Plant Lab" CO2 test kit, a Hagen
> alkalinity test kit, and a Tetra pH test kit. I took readings and they do
> not sit anywhere on that chart. I'm not questioning the chart's validity,
> but what can be the cause? My measurements as of 9:30pm last night:
> CO2 - 48ppm = 48mg/L
That looks suspiciously high.
> Alkalinity - 70ppm = approx. 4deg kH
> pH - 8.0!! (should be around 6.5 according to the chart, assuming the other
> values are true)
> Something is not right. I trust the pH test kit because how can you mess
> that up?
Reasonably reliable test.
> I trust the alkalinity (I think) because it is a titration process
> with a very unambiguous color change.
> I'm not so sure about the CO2 test
> kit because it is a titration process with quite a very gradual color
> change. (but it must be sorta close, right?)
Inherently terrible test. The reagent (not the indicator) is
extremely dilute sodium hydroxide. This absorbs CO2 from the air and
becomes even _more_ dilute. I would only trust this one if I calibrated
it immediately before I used it.
Paul Sears Ottawa, Canada