I see nothing on it that says submergable. It also only has one water line very near the top. Is this a minimum line or a maximum? I filled the tank very fill today during a water change, wich covered the top of the heater. It seems to be working ok still, but now it has water in the heating elements. Is it suppose to operate this way and I have been running it dry this whole time? Or is this one non submergable and now I've ruined it.