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



Yep. KH can shift from a lot of things. I added peat to my tank and it shifted down about a degree in a week. It's now shifting slowly up after an additional 3 weeks. I'm using products from the hobbyist market to make those measurements -- Aquarium Pharmaceuticals test for KH and Milwaukee pH meter. It's not like using "real" lab instruments. I figure the measuring error is close to equalling the shift in KH, and that I'm only guestimating the concentration of CO2.

That's mostly why I think that Tom Barr is generally dead on in his statements -- I can't really measure things well enough to give me any edge over his estimative methods. A half a degree of KH and .1 pH off makes a big change in CO2 concentration, and that's the best I can possibly measure. The picture is even more clouded if you are takling about measuring NO3.

Liz


Getting back to the tanks :-), you would need to remeasure
the KH after any introduced acids have had a chance to work
on the carbonates before you measure tried to use the
table, no?

And I guess the same could be said for any organically
produced acids in the tank -- so over the course of a week
or two, the organics might deplete the carbonates and then
testing for the pH and not the KH could then give wrong
results on the table, yes?

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

> 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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>
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