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Re: KH falling

To: Aquatic-Plants at actwin_com
Subject: Re: KH falling
From: Paul Sears <psears at nrn1_NRCan.gc.ca>
Date: Thu, 28 Mar 2002 18:19:37 -0500 (EST)
In-Reply-To: <200203281957.g2SJvPQ26406 at acme_actwin.com> from "Aquatic Plants Digest" at Mar 28, 2002 02:57:25 PM

> Date: Thu, 28 Mar 2002 14:29:39 -0500
> From: "Wayne Jones" <waj at mnsi_net>
> Subject: Re: KH falling
> 
> 
> I take it that this means that calcium will not precipitate if there is
> even a little disolved CO2 present.

	Any solution with carbonate or bicarbonate will also have
_some_ CO2.  The equilibrium reactions see to that.  The amount
of CO2 may be very small.  Calcium carbonate won't precipitate if
the product of the Ca++ and CO3-- concentrations is below a certain
value.  If the CO2 concentration is high enough, then the pH will be
low enough that the CO3-- concentration is low enough that CaCO3 won't
precipitate.

> I also take this to mean that if CO2
> is added again that it will just redisolve the calcium and the KH will
> just return to where it was?

	Yes.

-- 
Paul Sears        Ottawa, Canada

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