re: test kit and CO2

---------- Forwarded message ----------
From: psears at emr1_NRCan.gc.ca (Paul Sears)
Message-Id: <9702181451.AA21434@emr1.emr.ca>
Subject: Re: test kit and CO2
To: Aquatic-Plants at ActWin_com
Date: Tue, 18 Feb 1997 09:51:15 -0500 (EST)

> From: jcochran at pinc_com (John Cochran)
> Subject: test kit & C02
> I'm wondering if anyone can tell me if the Aquarium
> Pharmaceuticals water hardness kit measures GH or KH. The regents are
> labeled sodium hydroxide and calmagite solution.

	There is a third reagent as well - the EDTA solution that you
use to do the titration.  You are measuring Ca++ and Mg++ (together) with
this, so it is a "GH" kit.

> The PH of my tank has settled nicely down to 6.8-7.0 but the PH of the
> water used in my weekly 25% water changes is up around 7.4.  I'm worried
> that this might be too much of a shock on the system especially with some
> of the more sensitive plants prone to metldowns such as crytocorynes.

	The numbers you give imply that your tap water has less CO2 than your
tank water by a factor of about 3.  (The difference in pH is about 0.5,
and log(3.16) = 0.5)  If you change 25% of the water, with water containing
1/3 as much CO2, the overall CO2 concentration will become:
	0.75 + 0.25x0.33 = 0.833  times what it was before.
	The pH should rise by -log(0.833), or about 0.08, which should not
be a problem.
	I'm assumung that the bicarbonate concentration in the tank and in
the repacement water is the same.  It should be very close.

Paul Sears        Ottawa, Canada

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