ALK: 7-8
Magnesium: 1350
Calcium: 400-420
Doing weekly water changes with a good salt should help to keep all your parameters in check. But if your corals consume more than what the salt is replacing then you will have to look at dosing the required stuff.
I myself use Seachem dry goods from JL, lots of stuff out there to choose from. I find Seachem Dry Magnesium, Calcium and ALK is very cheap, very easy to use and of high quality.
Here is the online calculator most of us use:
http://reef.diesyst.com/chemcalc/chemcalc.html