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Re: Kh pH Co2

In a message dated 3/31/1999 3:03:29 AM Central Standard Time, 
Aquatic-Plants-Owner at actwin_com writes:

>  So you say that KH has no influence on the availability of CO2.  In 
>  other words, pH can be reduced by CO2 increase, or increased by 
>  KH increase, but KH and CO2 do not influence one another 
>  directly.  In other words, there is no buffering going on?  Can you 
>  elaborate?  What happened to the buffering concept?  What am I 
>  missing? (And thank you so much for allowing us to blame the 
>  textbooks rather than ourselves!)

I'm no chem expert but I think I got this principle so I'll take a shot at it.
pH is the balance between acid and alkalinity
KH is the degree of alkalinity
CO2 is one form of acidity 

By adding CO2 you do not change the amount of alkalinity but the amount
of acidity.  Therefore you move the ration of acidity to alkalinity in favor
of the acid.  Since pH is the ratio you are moving the pH number down.

Where I think a simple formula can go wrong is when there other acids
that cause the pH shift other than CO2.  Say you have naturally acid water
with a pH of 6.5 and dKH of 7.  If you use these to determine the CO2
content you might be way off if most of the acidity is from HCl rather
than CO2.