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Re: CO2 having no effect

To: Aquatic-Plants at actwin_com
Subject: Re: CO2 having no effect
From: Paul Sears <psears at nrn1_NRCan.gc.ca>
Date: Tue, 30 Mar 1999 09:16:03 -0500 (EST)
In-Reply-To: <199903300848.DAA26474 at acme_actwin.com> from "Aquatic Plants Digest" at Mar 30, 99 03:48:03 am

	A couple of replies to the original posting on this stated that
having a high KH can stop the CO2 from reducing the pH.

	This has come up before, and it is not true.

	A higher KH will cause the pH to be higher for a given CO2 
concentration, but the pH _change_ is the same for a given CO2 change,
whatever the KH is.  Look at the tables, or, better, the equations discussed
recently.  The relationships are logarithmic, so by "change", I mean the
factor involved, not the number of ppm CO2 increase (or KH increase).

	An increase of a factor of 10 in the CO2 concentration will
decrease the pH by 1.  An increase of a factor of 10 in the KH (bicarbonate)
will increase the pH by 1.  

	If the CO2 is increased by a factor of "x", the pH will drop by log(x).

	Also, the higher KH will not stop the CO2 being available to plants.
The CO2 concentration in the water depends on the CO2 system and the rest
of the tank setup - the KH has no influence on it.  The misconception can
be blamed on a number of aquarium textbooks.

-- 
Paul Sears        Ottawa, Canada

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