It's hard to tell with that pic, but it looks to me like there is some cyano
on the rocks. If that's the case you have a high nutrient level in your tank. SPS
corals do not like high nutrients where it doesn't both LPS
as much because they come from higher nutrient laden waters. Unless you have access to a high tech lab, there is no way for the average person to test their nutrient levels.
Are you running carbon? If so, what brand, how are you using it and how often do you change it out?
Do you have a protein skimmer? If so, what brand?