If the tank has ever had copper in it, that can cause coral death. PC lighting cannot be used for SPS (except hydnopora, digitata, capricornis) and these will eventually die also. I want to be the only person not politically correct here. DO NOT USE PC LIGHTING WITH SPS.
Yes I have seen people keep some sps with PC lighting (they never had good growth and never had the correct colors and all eventually died) SPS thrive (live, grow, retain color and dont die) under high PAR lighting levels. I will not say use only metal halide only because you can use VHO and T-5 lighting which is another debate. But I will say that to have great success with SPS, Metal halide is the only way to go for now.
Low magnesium levels will also cause coralline to die off. There are more parameters to a reef tank that have to be monitored other than Ph alk and calcium. High levels of phosphate, residual metals and other aspects can cause problems for reefs. Not using Ro/DI water for water changes, Crappy salt, electrical charges, Copper and rust from bad pumps, Filter
socks not properly rinsed out before re-use, shallow sand beds, deep sand beds, no sand bed, types of algae that go a-sexual, pests and a wide range of problems can be the cause of your situation.
Kasei
