I touched this subject in a recent thread regarding Reef Raft corals (post #27)...
http://www.canreef.com/vbulletin/sho...d.php?t=109720
I like to keep a measurable amount of nitrate in my tanks, maybe 2-5 ppm. The SPS do have a richer color. Certainly not 30 ppm though - that's quite excessive.