I was successful with SPS for about a year and a half. I made a couple of changes to my system adding a second tank and an automatic water change system. Since then I have been having trouble keeping SPS alive. I recently purchased a few frags as a test, both acropora and birds nests. Within a few days I started to get receiving from the bottom and eventually they died off. My water parameters are excellent, pH 8.3, calcium 450, alkalinity stable at around 9.0. I check my phosphates with a hannah checker and recently saw .04 the only thing that I can think of is that my tank temperature fluctuates between 76.5 and 80° because we keep the house very cold at night. Could this fluctuation cause the problem. I am heating the tank with a cobalt heater in my sump rated for 100 gallons but the heater is only half submerged due to the level of water in my sump necessary to run my reef octopus which is approximately 6 inches. I am thinking that when I added the second tank heater may not be able to keep up with keeping the tank stable. Any thoughts appreciated