Calcium and GH = magnessium

[Patrice]

I am wondering, if i calculate they calcium in my freshwater aquarium and my gh, i can get the results of the magnesium with out mg test kit.

I have 17 ppm of calcium
and 100 ppm of GH

logic dictate, i have maybe 83 ppm of magnesium

100 - 17 = 83 ppm magnesium

 

[Patrice]

Can someone confirm this information?

 

[Patrice]

Still need help on this.

 

[Patrice]

realty no one?

 

[Patrice]

I still need to know if this is right.