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Re: [APD] Re: H3PO4 and Green spot algae

Thanks, Liz, 

Just to clarify,
the "teaching" on this list has been that the CO2/pH/KH
table relies on carbonic acid being the only one present.
So you are saying that that is false?

--- Liz Wilhite <liz_wilhite at hotmail_com> wrote:

> >Just a point in passing. Doesn't H3PO4 throw off the
> >CO2/KH/pH table? By depressing pH, it should make the
> table
> >show more CO2 than you really haveSomething to keep in
> mind
> >if you're putting acids in the tank other than the
> carbonic
> >you get from CO2.
> No.  Those tables are based on the Henderson-Hasselbach
> equation dealing 
> with the dissociation of weak acids.  If enough
> phosphoric acid is added to 
> impact the carbonate buffer -- and I doubt the amount we
> are talking about 
> does -- then not only will the pH shift but the KH will
> also shift.  So, if 
> you add enough phosphoric acid to cause a measurable
> change in the pH then 
> you should measure KH.  The equation is still valid.
> This is why various people try to remind everyone that
> you should 
> occasionally check KH and GH even though they appear
> stable.
> The effect is probably not going to be all that much
> different than adding a 
> substantial amount of KH2PO4 or K2HPO4 to a tank.

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