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[APD] Re: Total DIssolved Solids vs General Hardness

On Fri, 18 Feb 2005 11:58:35 -0500, David Grim wrote

> I'm getting a TDS meter for the fish, but was wondering if TDS and 
> GH are the same thing or different?


GH (general hardness -- leader of the 3rd hardness brigade) measures the
concentration of calcium and magnesium.  Nothing else.

TDS (total dissolved solids) measures everything in water that is left when
the water is boiled off.  If you use a meter then that result isn't quite the
same thing.  With a meter you measure a quantity related to the total
concentration of charged ions in solution.  Either way, TDS includes calcium
and magnesium.

You can have 0 GH in water with a lot of TDS.  You can't have 0 TDS in water
with any GH.

Roger Miller
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