Re: Other acids and CO2-pH-KH table

[George Booth <booth at lvld_agilent.com>]

Adrian Banica wrote:
>I have been looking at the carbonate buffering system in fresh waters in
>detail and I had one silly question really. We are all familiar (and trust)
>the CO2-pH-KH table (I have done tests myself, I have to be convinced). But
>now what happens when we start getting some accumulations of byproduct acids
>such as tannic, humic, nitric, etc? All of these will dissociate to various
>degrees until they reach their own particular equilibrium points. Will this
>now render the CO2 chart pretty much useless? 

Some of these byproducts in typical aquarium concentrations may render The Chart 
very slightly inaccurate but probably not so much that you would notice, given 
the typical accuracy of pH, KH and CO2 measurements. 

>Or will the extra H+ generated
>just combine with the HCO3- and slowly exhaust the akalinity?

Yes. This is the usual cause of a "pH crash" in a poorly buffered tank. As it is 
being slowly used up, the pH will vary only a little. When it's almost gone - 
Whammo!

Regular water changes help maintain byproducts at insignificant levels. Regular 
KH checks and adjustments compensate for slow usage. 

We have found KH consumption by normal aquarium processes to be minimal over a 
two week period (between water changes). Given the accuracy of our test kits 
(LaMotte), we saw no change. The details are in the archives somewhere. 


George Booth in Ft. Collins, Colorado (booth at frii_com)
  http://www.frii.com/~booth/AquaticConcepts 

PS: My home computer is still down. If you have written to me at frii.com, I 
have been unable to read it. Maybe some day the @$%&#$ warranty company will be 
able to fix it.

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