# GH and Ca/Mg



## niko (Jan 28, 2004)

Ok, the General Hardness (GH) is a measurement of mainly the Ca and Mg ions in the water. One can easily find tables that show the conversion from dH (the units in which GH is usually measured) to ppm. 

Since both the Ca and Mg are important in growing healthy plants it seems that we need to be more aware of the amount of these 2 elements. 

Say I have GH=4. That means that I have 70 ppm of Ca and Mg. 
How much of the 70 ppm is Ca and how much is Mg? Could I have 90% Ca and 10% Mg? 

Also - should the Ca to Mg be kept in a specific ratio? 

--Nikolay


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## Error (Apr 16, 2004)

If you're up for a little algebra, here's a formula I found:

ppm CaCO3 = ([Ca ppm]*2.497) + ([Mg ppm]*4.116)

I found it here.


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## gnatster (Mar 6, 2004)

1.648378053664397276732078494193 Mg : 1 Ca

Is that right?


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## Error (Apr 16, 2004)

Got me.

I failed algebra


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## Steve Pituch (Jan 25, 2004)

Hi all,

No, the equation does not specify a specific constant ratio of Ca to Mg. It is infinitely variable. You could have any proportion of Ca/Mg at any hardness.

However, if you knew the hardness and either the Ca or Mg concentration, you could figure out the other.

Steve Pituch


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## niko (Jan 28, 2004)

Ok, simple enough - check the GH, the Ca, and calculate the Mg.

So what would be good Ca and Mg levels?

--Nikolay


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## IUnknown (Feb 24, 2004)

Lamotte sells kits to measure each. I've read 4:1 Ca to Mg, and I've read the other way around before, so..


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