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Hardness and Units

>Date: Wed, 24 Jun 1998 16:58:47 -0500
>From: George Slusarczuk <yurko at warwick_net>
>Subject: Re: Aquatic Plants Digest V3 #341
>Hi Steve,
>I would like to second your suggestion to use ONLY metric units. There
>are only two years left to do it in the 20th century!

I personally do not think there is a problem, per se, with GH and other
hardness units presented in "degrees". For the mass market, it is quite
useful and for people including myself who do not like the time and trouble
it takes to use a test kit, I like the simplicity of the Tetra test kit (1
drop per degree until the color changes). As indicated by the Forest King,
the level of precision is good enough for OUR purposes. 

In the dynamic space of a relatively small planted aquarium, I would only
need more precision and accuracy if I was trying to monitor Ca levels in
very soft water (< 1-2GH or 7-14 ppm Ca)

I do like to know what the ppm levels are. So, my preference is to report 2
sets of units - degrees AND ppm (or vis versa). This should satisfy almost
everyone. IMHO, it can be counter productive to get rid of a set of units
that has such a long history in the aquarium industry. There is a lot of
useful, old literature that will never get reprinted.  If I were marketing
the LaMotte or more sophisticated kits, however, I might just report in ppm
(or mg/L). But, a note in the instruction sheet about alternative units,
including degrees and CaCO3 equivalents would still be helpful. 

The best that I can figure is that 1 German degree of general hardness (GH)
 is defined as 10 ppm CaO which has 7.14 ppm Calcium. Any comments or
corrections are welcome.
One of the biggest problems with use of degrees is incorrect or misleading
conversions (so, I hope I got it right<g>).  When conversions from degrees
are made, it is important to know if we are converting to Ca, CaO or CaCO3.
I think this has been one of the greatest source of confusion. This
determines if we  multiple by 7.1 or 10 or 17.9. (It is also not always
clear how Mg salts are reflected in these conversions) Perhaps a chemist
can step forward and provide some assistance or additional clarification.

Neil Frank, AGA