Have a look at this, you need to keep 3 levels in check, Kh, Ca, and Mg.
http://www.reefkeeping.com/issues/2006-02/rhf/index.php
you can buy it here, and Red Coral has it I believe. (not that your in Calgary though)
http://www.canreef.com/vbulletin/forumdisplay.php?f=67