Be careful about how you are using unbalanced amounts of the Ca and Alk parts. Ca and Alk have a complex interrelationship that cannot be ignored. Increasing Alk too quickly and too much can pull down your Ca. Also, you must make sure that your Mg levels are where they should be or your in for some frustration. The key is to take things slowly and do a lot of testing and notation of results.
Here's some more fun reading:
http://reefkeeping.com/issues/2006-06/rhf/index.php
See also the additional links at the bottom of that article, specifically from this:
"If an aquarist is supplying a balanced additive to his aquarium, and calcium seems stable but alkalinity is declining, it may very well be that what is needed is more of the balanced additive, not just alkalinity."
which is taken from this article:
http://reefkeeping.com/issues/2004-12/rhf/index.php