I had a coral not opening in my ten gallon last week. No big deal, sometimes that happens with one coral or another for a day or so here or there, once in a great while. A few days later another. So I did a water change just for the heck of it, just in case. A day or so later several and things were looking pale, did another water change and started to get worried. Next day, yesterday went to do another water change and the tank water was wayyyy warm. I dont have a themometer on that tank. Took its temp and it was 86.6! I got to looking and my heater was stuck on! I did the water change and put in a different heater and slowly brought the temp down. I rarely test my water or have issues because I do very regular water changes. I was about ready to start testing the tank up and down when I saw what the trouble was. I have never had a Cobal heater get stuck on, ever. What a scare and I still dont know if my corals are totally out of the woods as some still look peak-ed, not open yet and lighter in color than they should. Some still not opening. I pray... with consistant good care and patience, they will come back around. I have never had a tank crash, Praise God but this sure scared me. I love my corals and little critters. I would hate to ever lose any of them.