I dose these from Seachem.
http://www.seachem.com/Products/prod...eefBuffer.html
Keeps PH up as well.
http://www.seachem.com/Products/prod...dvCalcium.html
Adds Mg as well as Ca.
I keep my alk at around 8 KH, and Ca around 400. Mg is around 1300. Using IO salt for now.
My tanks remain very stable, and have not had to adjust my dosing for a couple months now.