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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