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Re: Alkalinity and Phosphates

Roger Miller said, in part:

> . . .Possibly the most consistent indicator of a problem
> be had by using a direct CO2 test.  If the CO2 determined
> by the KH-pH method is significantly higher than the
> results 
> of a direct CO2 test then there may be some extra form of
> alkalinity in the water.
> I don't know that the CO2 test kits are any better than
> the
> KH-pH method.  The direct tests for CO2 are actually
> "acidity" 
> tests.  The test depends on the assumption that the
> measurable 
> acidity is caused by CO2.  By contrast, the KH-pH method
> assumes that the measurable alkalinity is all caused by 
> bicarbonate.  The assumptions are very symmetric.  Both 
> methods are subject to the same kinds of interferences,
> though
> from different sources.

My experience with the Hach CO2 test is that the changes in
color (it's a titration test for a color change) are very
subtle, so much so that readings need to be "generalized"
as a range of about plus/minus 5 or so parts ppm.  Put
another way, the difference between not purple and purple
is very gradual:  Is that purple yet?  It think that's
starting to turn purple. No that's not purple; add some
more drops.  Well it's sort of purple now; add some more
drops.  Well now it's definitely faintly purple. How many
more drops was that?  Nine? Ten? Twelve?

Anyway, if you have organic compounds, don't you have acids
and those goof up the results using the pH/KH/CO2 table --
but then wouldn't those same acids cause a (false) high
reading on the CO2 titration test?

Just to be clear, the organics cause a false high reading
on the KH tiration test?

Scott H.

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