I've got a 550g Reef Tank. The candy cane corals are having the flesh fall off their heads. The flesh does not die for 1-2 weeks. The other problem is montipora corals don't live more than a week. Calcium is 430ppm, Alkalinity is 8.9 dKh, Magnessium is good. Tank is skimmed with a Deltec Skimmer and Maintains a temp of 80 with a chiller. The lighting is 3- 400 Watt Mogul Metal Halides 14000K and 4-250 Watt HQI 20000K. Any ideas on what could be causing this. Thanks.