Aquarium heaters are dangerous !

[Philsuma]

They are IMO.

I've used them for egg and tadpole incubation tanks and they are always prone to hot spots and malfunctions.

I guess, like anything, there are cheap ass models and very $$ models that are more reliable. I still wouldn't use them.

The other problem, is that when you use a fish tank or aquarium heater in a fairly shallow or small water area - bad things can happen a lot quicker than in, say, a fully filled 10 gallon aquarium ect. Hot spots and malfunctions can kill eggs and tadpoles in a matter of hours.

just my .02