[emc7]

I lost a fish today (fine yesterday) to a heater to the first time in 2 decades. The 10 gallon tank was 94 degress and the Tetra Whisper 10 heater had its little red light on. It wouldn't go out no matter how far I turned the knob to the left. I used to like this model becasue it was cheap an the cover kept the knob from getting bumped and becasue it has a pretty good heater clamp. I will never buy another. I like submersibles better anyway. I took it apart and instead of being sealed to the glass like I expected, there was only a thing like a rubber stopper inside and a rubber band like thing outside. I don't expect hang-on-tank heaters to be water-proof, but water-tight would be nice. To be fair, I didn't find any water in the tube, it looked like it had just cooked itself. I've had the little 50W whisper heaters fail before, but always by not heating. One reason not to use an oversized heater is that if it malfunctions, it will cook your fish more slowly. But I am now thinking that the littlest, cheapest heaters are more risky..