Well I bought a heater for my 50gal about a week or so ago and it was working fine at first. I had the tank at a really stable 78 for about a week and then last night I was doing a water change and noticed the water was REALLY cold so I look at the thermometer and it said 68! So I try to turn up the heater and it usually clicks on and has a little light but it didnt to anything so I tried to unplug it and plug it back in and still nothing so I pull it out and I see about an inch from the top it has crack in the glass that goes all the way around and then it is filled with water. How could something like this happen? I forget the brand but I know its one of the best you can buy from the pet store I bought it at. (It was the best that isn't made for a saltwater) and I don't want to go pay another 40 if its not going to work. Oh and I thought maybe like a fish or something hit it really hard but I don't have any fish that are big enough for that. I have 3 parrots, 3 silver dollars, 3 green severms, and a 6in common pleco. Any ideas as to what happend? EDIT: Oh and the heater is in between the side of the tank and a filter so the fish can't really get to it anyways.