So yesterday I came downstairs in the morning to find my acans frag, which I have had for about 2-3 months, had totally melted away, leaving just a skeleton. The day before it looked healthy. My green favia brain, which is in a distant location from the acans, is also starting to peel away from its skeleton, in obvious trouble. The other LPS and SPS in the tank seem fine. Tank parameters - amm/nitrite/nitrate 0, phosphates 0, pH 8.0, calcium 460, magnesium 1500, alkalinity 4.5 mEq/L, temp usually ranges 77-81, salinity 1.025. The things that have changed - my tank had been fallow for 8 weeks and my fish were returned to the tank 2 days before. However, I have been monitoring the tank parameters very carefully and detected no spikes. Also, the night the acans melted away, I had a thermal malfunction where the temperature dropped from 81 that it had been during the day to 75 degrees at night (usually only goes to 78 at night). So bottom line question....why the coral deaths? If it was an ammonia spike (which I doubt), why only the acans and favia affected and not the LPS/SPS? If it was the temperature, same question. Any other suggestions? Solutions?