Just don't understand

[reeferdon]

I don't understand how my system uses alk and cal but not as much mag.
I use Aqua Forest reef salt and test kits, maybe my mag test kit bad. Waiting on icp test.

 

[NY_Caveman]

Magnesium is less of something used as something where the appropriate level allows for optimum use of Calcium and Alkalinity. Check out these by @Randy Holmes-Farley

http://reefkeeping.com/issues/2006-06/rhf/index.php#21

and this

https://www.advancedaquarist.com/2003/10/chemistry

 

[Donsreef]

So when is the best for testing the 3 elements?

 

[Randy Holmes-Farley Verified Community Expert]

So when is the best for testing the 3 elements?

You mean time of day? it doesn't matter.

The rate of magnesium consumption is typically 1/10th of the calcium rate, or less. So in many tanks it is well below 1 ppm per day and is very hard to see with a kit.

With water changes and a high magnesium mix, you may never see a substantial decline in magnesium. That said, if you are using my DIY two part, I'd use it anyway. It is not just for magnesium. and if you wait for magnesium to noticeably decline, you might need to add back as much as you would have been adding all along..