Zoo Med BettaTherm 7.5W Submersible Aquarium Heater for Small Fish Tanks & Betta Bowls - Perfect for Tropical Fish, Shrimp Tanks & Nano Aquariums

I almost gave up on finding a heater that actually lived up to the standards in their descriptions. Two others that I tried never went past 72 degrees, although the descriptions said they went to 78 degrees. This little BettaTherm heater is the absolute best. It stays at a consistent 79-80 degrees. My Betta, Clifford is just thriving in his 2.5 gallon bowl. He is so much more active since I put in this heater. This heater takes up no room, is flat and covered by your rocks on the bottom of the bowl. There is a suction cup that holds the cord nicely against the side of the bowl. I would say..stop looking at other heaters, this is the best out there.