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Re: [APD] KH question

I know I should let this pass but...

Adding carbonate does buffer the system. A buffer solution contains a weak
acid and its conjugate base. Carbonate is a base which reacts with water, an
amphoteric substance, forming bicarbonate ions and clusters of water
molecules of various numbers and shapes that have hydrogen ions associated
with them.  The conjugate base of bicarbonate is carbonate. If you add
bicarbonate to water, it also reacts with water forming carbonate ions and
those same clusters of water molecules with hydrogen ions.

Adding CO2 to water forms "carbonic acid" which is either an incredibly
strong acid or a pretty weak acid, depending upon how you define "carbonic
acid."  The dissolution of CO2 in water yields a solution containing water
molecules associated with hydrogen ions, bicarbonate and carbonate ions.

The addition of carbonate (or bicarbonate) ions to water creates a solution
to which an acid can be added without a large change of pH -- i.e. it
creates a buffer solution.

I was just looking to know if anyone with a relatively low KH had suffered a
pH crash as a KH of 3 indicates a reasonably low concentration of carbonate
and bicarbonate ions in solution, even assuming that there are no other ions
interfering with the KH test and I'm not certain that is a valid
assumption.  I appreciate knowing that you haven't had any troubles so I
shouldn't expect any, either.

On 11/19/06, Vaughn Hopkins <hoppycalif at yahoo_com> wrote:
> Where I live now my tap water has KH below 1.  I don't add anything
> to "buffer" it.  I use 40 ppm of CO2 in the tank, and the pH hasn't
> changed enough to cause either the fish, shrimp or plants to complain.
> Incidentally, to buffer a solution requires adding a substance that
> resists increases in pH and a substance that resists decreases in pH
> - always two substances.  Adding just one, like bicarbonates, only
> shifts the pH higher, it does not buffer the solution to a specific pH.
> I just felt a need to be pedantic there.  Sorry.
> VaughnH.
> On Nov 19, 2006, at 10:20 AM, Liz Wilhite wrote:
> > I moved recently and went from tapwater with a KH of 9 to tapwater
> > with a KH
> > of 2.  The KH in the tank with aragonite is about 6, but the Eco-
> > Complete
> > tank is running about 3.  I am just getting my CO2 up and running
> > again and
> > I have a question:  with a KH of 3 do I run a risk of the pH
> > crashing?  If I
> > need to raise the KH, could I expect to see a consistent, stable KH
> > level if
> > I added a bit of crushed coral to the canister filter?
> >
> > Thanks.
> > --
> > Liz
> >
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