Rapid Tissue Necrosis. I bet the water chemistry is different between the two. Do new sps make it in your half circle tank? I run a half circle tank too...144 half circle running 3 AI Sols and 6 panorama pros so total about 340w of LEDs. I have several montipora doing just fine...no bleaching. One is about 15 inches across....is that what you'd consider show size? My tank is 90 percent sps and rarely do I have any new additions bleach or RTN....check your water chemistry, alk is the first thing I'd check. Do you run dosers or a reactor?