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Re: [APD] GH vs. PPM



Liz wrote:

> If the pH is X and the KH is Y then the CO2 concentration is always Z
> regardless of other acids present if you have a steady state that
> looks like an equilibrium.

This could be true, depending on your definitions.  It would be more accurate 
to rephrase this to say:  "If the pH is X and the bicarbonate concentration 
is Y then the CO2 concentration is always Z regardless of other acids present 
if you have a steady state that looks like an equilibrium."

The problem is that some "other acids" can be measured as part of the KH.  KH 
is then an inaccurate representation of the bicarbonate concentration.  Mono- 
and dihydrogen phosphates can have that effect but they -- without large 
intentional additions -- rarely reach concentrations high enough to be 
significant.  Probably the most common interference comes from organic acids 
that originate from wood and peat.


Roger Miller
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