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Re: GH Dilemma

Alex wrote:

> I've recently inquired my tap water supplier for some info about my water. I
> asked about Ca and Mg concentrations, and was told there was about 51 ppm
> Ca, and no detectable Mg.

That's odd -- possible, but odd.

> My GH test kit measures 80, or about 150 ppm.
> That's what I told the water company representative, and he replied that
> their Total Hardness value is about the same.

True.  Their 51 ppm calcium equates to about 128 ppm hardness, or just a
little over 7 degrees.

> The difference, he said, was
> because a GH test measures other cations in addition to Ca and Mg.

Uh, barium and strontium anyway, which should never be significant.  I
don't think that's the problem.

> So my
> question is, when determining the true value of my GH, do I use the results
> of my test kit, or the 50 ppm of Ca (+ 0 Mg)? Or is there a difference
> because GH is really measured in CaCO3?

Probably the difference is because of your test kit design.  A titration
kit that measures in 1 degree increments can be wrong by as much as 1
degree.  When you read 8 degrees GH the actual value can be anywhere
from 7 to 8 degrees.  The utility's reported calcium level gives just
over 7 degrees GH; a kit that reads in 1-degree increments should read 8
degrees.  My utility consistently reports that my tap water contains 7
mg/l of calcium and 1 mg/l of magnesium, which translate to 1.2 degrees
hardness.  My test kit consistently reads 2 degrees, as it should.

If your kit reads in ppm, then you have the same problem, but the steps
are in bigger numbers.

Roger Miller