This is my first time using an aquarium heater. It is a National Geographic brand 50w heater. I've read the manual and asked the pet store employees but no one can tell me what the MAX water level is. The MIN level is clearly marked. It has a temperature selection ring on the very top where the cord attaches and I just need to know if that entire part can be submerged, as that is the only way I can close the hood on the tank.