I just had a cobalt neotherm heater blow up in my sump!!! I heard a loud noise, and thought it was my dogs. I walked out into the living room where the tank is and my dogs were smelling that area. I got closer and smelled smoke. Then I could see smoke!!! A lot of it! I opened up the cabinet to the sump and smoke come billowing out! I looked at one of my heaters and saw that it had exploded under water! Fortunately, I just got home from work or this could have been worse. I also just have two shrimp, a crab, and one chromis. They should be okay... I hope. My gfci didn't even trip though.