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Re: [AGA Member] Water question..

Besides not being a very good typist, I am not a chemist. 
But I think I can help a littel bit here.

CO2 does not affect the KH, nor does KH affect the amount
of CO2.  They simply have opposite effects on pH, so if you
know the value of two of the items, you can calculate the
third, or look it up in the appropriate table. But it seems
you are getting at something else -- low CO2 causeing
plants to use up carbonates and thereby decrease KH.

It's true some plants can get carbon from carbonates in the
water, although I think that those that do, do so when CO2
is limited. The CO2 is easier for them to process.

The KH in the water can lower if plants are using
carbonates - vals being one candidate -- but it can also
rise if the substrate is one that adds to the hardness or
if you are adding chems that raise the carbonates -- the
latter apparently not the case for your situation.

But the KH level should not cause the CO2 to be higher or
lower. So, if you are not injecting CO2, then the KH might
lower over time, which I gather is what you are getting at.

Basically for the reasons Rachel pointed out, tap water is
not a good source of CO2 and probably does not factor
largely into the use of KH.

Chemists, jump in and comment/correct me here.
Scott H.
--- Amit Brucker <amitb@gtek.co.il> wrote:
> I know of course that CO2 had a direct effect on PH,
> However  I am more
> interested in the connection of KH and CO2, as it seems
> that high KH levels
> can contain higher CO2 levels than lower KH levels....
> And since what effect
> KH are carbonates and bio carbonates and that plants may
> use (Maybe I get
> this one wrong...) I was wondering whether less water
> changes will lead to
> decrease in the KH levels as CO2 will drop. (thus while
> maintaining a stable
> Ammonia/nitrite levels).
> Hope I've made my self clear

See you in Dallas at the Aquatic Gardeners Associaton
2003 Annual Convention
Nov 14-16
S. Hieber

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