Pockets - i can't answer your question directly re Nutri-Calc, but alternatively I wanted to show you two very educational links I just recently found.

The first discusses the relationship between Magnesium and Calcium and what you should/shouldn't be worried about, and also some dosing calcs:
http://www.aquaticplantcentral.com/f...ationship.html

The second discusses more just the calculations of dosing:
http://www.aquaticplantcentral.com/f...cl2-mgso4.html


I know that doesn't directly answer your questions, but I hope you can find them useful.