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Re: George on the soapbox again


Date: Tue, 16 Jun 1998 10:51:49 -0500
From: "Douglas W. DeSimone" <dwd3m at avery_med.virginia.edu>
Reply-To: dwd3m at avery_med.virginia.edu
To: Aquatic-Plants at actwin_com
Subject: Re: George on the soapbox again

I'm not sure I want to get in the middle of this interesting discussion
but as someone who also keeps a reef tank where Calcium dosing is
critical I'd like to comment on one question posed by Steve:

Steve Pushak writes:

"Clarify for me if you will, how to determine the calcium concentration
from a GH measurement, please George? Could you also explain how to get
the magnesium concentration??" 

The HACH total hardness and Calcium kit (cat# 1457-01), with which I am
most familiar,  allows one to determine "total hardness" and Ca hardness
expressed as CaCO3 in mg/l.  With this kit, Mg hardness in mg/l is
"determined" simply by subtracting the calcium hardness from the total
hardness value. As I understand it, total hardness in most "natural"
waters is contributed almost entirely by Ca and Mg ions.  Although kits
such as the HACH (using EDTA titrants) also register other di- and
trivalent metals, these are typically quite low in most water sources. 
(Note that iron can also interfere with the kit but not at the
concentrations typically present in fertilized plant tanks.)  While it
is critical to sample Ca levels in a reef tank with some frequency I
haven't found this level of information to be of particular value for my
own freshwater plant tanks (i.e., assuming a "stable" municipal water
source, and regimen of water changes as Steve suggests) .  Given the
price of the HACH and similar kits, I certainly wouldn't recommend them
for "typical" aquatic gardeners.
	Also, IMHO I would prefer to see mg/l values used generally as opposed
to ppm in most discussions of water parameters although I realize this
is not possible with many test kits.

Doug DeSimone
University of Virginia
Department of Cell Biology
Box 439, School of Medicine
Charlottesville, VA 22908
dwd3m at virginia_edu