Review on SunGrow Halfmoon Betta Heater: Efficient 10W Submersible Aquarium Heater with Preset Temperature Control for Small Tanks by Lance Levatte

Excellent heater. It's very thin and takes up almost no space in my 1.5 gallons. It does an excellent job of maintaining water temperatures of 77-78F. This heater is handy in that it isn't "on" all the time - it senses the temperature of the water and gradually turns on to maintain the temperature. That way the tank doesn't overheat. You can tell the heater is on by the handy red LED at the top. To get it working I recommend rinsing it, placing it in the aquarium for 10 minutes and then plugging it in.