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



Yes. H-H is used widely in medicine. CO2 concentrations in blood is determined from knowing the pH even though there are significant quantities of PO4 around. The reason most of us pant after running up the stairs is from acidic metabolites entering the bloostream. We pant to get rid of excess dissolved CO2 thereby raising the pH back to normal. At least that's what I understand -- I'm not a doctor but I was once a chemist.

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?

sh
--- 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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