I know this thread is over a month old, however I would like to add the importance of magnesium in the ionic balance of Calc, Alk and Mag. These three are completely interedependant and inorder to keep one in check they all need to be in check. Mag is very easy to dose (epsom salts) and here is a great little reef chemistry calculator that might help.
Reef Chemistry Calculator

Additionally you might want to reconsider salt brands. Here is a great little study on salts and their contents of each mineral.
http://www.aquariumwatertesting.com/...lysis_0208.pdf