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Re: CO2 will depress the KH?

> From: Boulet Stephen-CSB046 <Stephen.Boulet at motorola_com>
> Subject: True or false?
> True or false: with CO2 injection, a tank with a kH of 5 will be depleted of
> calcium hardness in a matter of days by the carbonic acid if no extra
> buffering is added, causing the pH and CO2 concentration to drop?

False. CO2 is a WEAK acid. If you added a strong acid (say like HCL) it
would remove the KH and then your KH/pH would drop.
CO2 cannot remove KH and KH cannot evaporate or outgas. It can be removed by
a strong acid or RO/DI filter etc. Your KH is fine though.

 Plants can and do use KH (-HCO3) as a carbon source. If you have enough CO2
for the plants in the tank they will use that instead of the KH(-HCO3).
They'd rather use the free CO2 in the water but will switch to the -HCO3 if
they have to. Many plants cannot use -HCO3. Hornwort, Egeria, Potamogeton
etc can. You get CaCO3 and perhaps some other carbonates building up on the
leaf's surface from the usage of HCO3->CO2 (for the plant) + -OH. The -OH
builds up on the leaf's surface and raises the pH very high(the CO2[acid] is
removed)which causes the Ca to precipitate out on to the leaf's surface as a
deposit. These deposits are collectively called marl.

> I'd appreciate some comments on this. What do people use for buffering?

You don't need any. Baking soda, potassium bicarbonate, crush coral,
Just add the CO2 correctly(get your pH to 6.8 and keep it there). You will
have nothing to worry about on this issue. Also, if you do water changes
every 2weeks or more often you have nothing to worry about.
Tom Barr
> - -- Stephen