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Richocet83
07/23/2015, 08:46 AM
Does this equation hold true with marine water???

[CaCO3] = 2.5(Ca) + 4.1(Mg)

The reason I ask is I have a photometer and reagents for Total Hardness and Calcium Hardness but nothing for Mg and figured I could get Mg by using this equation. Unfortunately, when I compare the result I'm getting with a titration test on Mg they're not even close.

On photometer I'm getting: Total Hardness of ~285ppm (this was diluted x10, as our photometer will only read to 600ppm) so Total Hardness = 2850ppm (which seems awfully low).

Ca Hardness was 1025, divided by 2.5 = 410ppm

So based on these numbers I should have a Mg of about: 445ppm

Using a Red Sea Titration kit I get a Mg of about 1120ppm.

Any help would be great.... I'm not a chemist and I don't play one on TV either.

Thanks!
-Ryan