I use a home made 2 part, actually 3 part as I test for and dose magnesium. I believe B-ionic is the best, but it gets real pricey when dosing 2 cups of each part a day.

http://reefkeeping.com/issues/2006-02/rhf/index.php

To purchase calcium and mag, I go to our sponsor.

http://www.buckeyefieldsupply.com/