98 degrees

just got home from work ,walked past my 40 gal freshwater aquarium , looked at the temp ,and it was 98 degrees in their , couldnt believe it , the thermometer was set at 80 for over a year know .and never touched. All the fish acted normal .did a 5 gal water change of a cooler temp water and set up my chiller.Slowly the temp is dropping , i also noticed the temp control was moved . the only thing i could figure is , i have a 6 inch pictus catfish thats a little spastic, when i feed my fish he is all over the tank .maybe he hit the control. ive heard b4 that when you walk by your aquariums you should touch the glass once and awhile to make sure. relieved , ive had these fish for over a year and they have grown on me. very strong fish. disaster aborted!

Not sure how they didn't die at that temp, that's crazy. I can't imagine there was any oxygen in that tank. This is exactly why I don't run any heaters. Not even on my reef tank. I've had heater malfunctions in the past and it killed everything.... Glad to hear they somehow made it through.

Yep heaters I keep for emergencies only. They all have a thermostat, so its gonna stick in a spot and stay there after a few years. All of them do it eventually some just do it sooner then others. I let my tanks get down to 65f and no lower, if it does one of my 3 heaters gets pulled out and used.

65? at what temp does the good bacteria start to die? one could just use a heater thats undersized for the aquarium so that if it did malfunction then would not get warm enough to kill anything..I do use heaters cause if i didnt i would have to turn up my home heater to warm the room up enough to get my aquarium water to 76 or so and thats exspensive here in the winter time

Nitrobacter have an optimum pH between 7.3 and 7.5, and will die in temperatures exceeding 120°F (49°C) or below 32°F (0°C)