Its submersible, and the top is about 1-2 inches from the waterline. I know its not water quality cuz I have him in fin rot treatment so he is getting daily 100% changes. The part he was laying on was something that wasnt emitting heat so i dont think it was for warmth although the tank is waiting for a new heater cuz the current one only gets to 76 max.
EDIT: I came back from an overnight trip and noticed it this am. Last time I fed him, he ate (he likes to dive for the pellets as they start to fall) 2.5 gallon, and no tank mates