I'm looking to replace the heater in my 5 gallon. Right now I have a submersible heater rated for 2-5 gallons, I can't remember the brand or the wattage. But its a preset heater, and I would like to find something more adjustable because it barely gets my tank above room temp. Anyone have any suggestions? I do prefer submersible heaters, but that isn't a necessity.
Maybe try a 50 watt submersible, i believe you can get them in adjustable models. Just checked Foster& Smith. Marineland makes a 25 watt submersible, adjustable heater. It is rated for 6 gallons. might be what you are looking for