I have a Marineland Visitherm heater and it claims to be "submersible". I have always been a bit reluctant to put heaters completely underwater. Still, I know I have seen people with their heaters attached way down at the bottom of their tanks, lying horizontally. Can all aquarium heaters do that? Or do those say something like "fully submersible"?
For reference, that's the heater.
For reference, that's the heater.