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Re: [APD] CO2 measurement

Hi Tom, we have discussed this a bit on your site.

I know you keep saying it's CO2 but..

My city water report says KH is due only to bicarbonate, and that the KH 
is 18.  AP test kit confirms this value.

Two different pH test kits agree my pH is 6.8.

I find it difficult to come to any other conclusion than that my CO2 is 
at or around 85 ppm.

Most all my fish are fine and happy but three that were probably already 
weak were up at the surface.  I figured since the others were just fine 
the CO2 was okay, but it was probably too high since it killed off the 
weakest fish.

Anyhow I have a bit of hair or thread algae, decent pearling, moderate 
growth.. I would say I can't complain.. but yes, I can!

Thomas Barr wrote:
> There's little issue with the CO2/pH/Kh table.
> The problem is in the measurement of KH and/or pH.
> Ph is fine if using a pH calibrated pen/probe etc and all the
> electrical devices are off or well grounded.
> Alkalinity test, the KH, measure only total alkalinity, not
> specifically carbonate hardness. So hydroxide, borate alkalinity
> and phosphate acids can play with CO2 determination as well as
> user errors.
> While seeking accuracy is useful in some cases, the reality of
> the tools to determine the method are quite another matter.
> It is not uncommon for careful aquarist to have 50-200ppm of CO2
> and healthy fish, while some might have 30ppm reading and
> gasping fish(generally due to low O2, but not always).
> Accuracy to 5ppm +, - is about the best folks can realistically
> hope for given the error of the best alklanity test kits sold,
> is about 4ppm.
> But.....even that assumes all the alk is bicarb, which is not
> always the case.
> Every method has a trade off and a set of assumptions.
> Some better than others.
> Rergards, 
> Tom Barr
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