DIY Calcium, Magnesium and Alkalinity Additives
 

I use the DIY two part additives detailed in this link. It is very inexpensive and effective. I found commercial preparations very expensive to use.

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

This link helps determine how much of these additives to use, based on tank volume. Select Randy's Recipe as your additive.

http://home.comcast.net/~jdieck1/chemcalc.html

Hope this helps!