I use the 2 part EVS B-Ionic. Component #1 - Carbonate Alkalinity, Component #2 - Calcium Concentration
I try to keep my calcium at 400, My kh at 8 and my magnesium at 1400.
You will need to test for calcium, magnesium, ph, and kh. All are effected by calcium additives. I use this website to figure out how much of each additive to add.
Reef Chemisrty Calculator
Hope this helps.