I second Pogodzib. Do ~20% water changes every other day for about a week. Make sure you use RODI water and let the water sit for 24 hours with some type of circulation and heating.
I like the 2 Part Kent Ca additive to supplement my tank; maggyboy is also right about keeping your Mg level up. I keep mine about 1400-1450 which helps control hair algae. I'll add about 1/2 the recommended dose of Kent's Trace Elements about every 4-6 weeks. (The full dose gave me problems with cyanobacteria).
These doses really brought the pink and purple out in my coraline algae, deepened the red in my Blastomussa wellsi/Lobophyllia as well as turned one of my dull brown acroporas to a deep peach color.
