Well here we go again, I somehow managed to forget to turn my heater of on a midnight water change in my fry tank (I blame tiredness). The heater was on a temperature of 24 degrees. I noticed after a couple of minutes due to a 'burny' smell and after turning the heater off I could hear it sizzling, it is completely exposed to the air. I can see no signs of damage and could do with a quick answer on wether or not I am safe to turn it on, this heater is in fact my spare. The fry would maybe survive room temp overnight but I really don't want to risk it, still, it's probably a better risk than electrifying the water.