I keep my Calcium between 350-400 personally (mainly because my source water has low calcium and I don't feel like adding Ca. to my water change water.) But 500 IMO is high and very close to the edge of where you want to be before alk starts suffering.
Couple of good articles to help explain where you need to be and how to get there:
A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH by Randy Holmes-Farley - Reefkeeping.com Chemistry and the Aquarium