Well it is less of a concern if you only have fish.
Some things to keep in mind though are that calc, alk, and mag play together and if you are very high on one your are likely low on another. Before you get any corals you need to straighten things out but do it slowly.
Here is some reading for you on the topic.
Reef Aquarium Water Parameters by Randy Holmes-Farley - Reefkeeping.com A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH by Randy Holmes-Farley - Reefkeeping.com A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH by Randy Holmes-Farley - Reefkeeping.com
Grr new computer so I know I am missing some of the really good ones. Try looking through past RS threads. We link to them often.