Review on 🐠 LEDGLE Submersible Aquarium Heater with Thermometer: Ideal for 3 to 5 Gallon Betta Tanks, Saltwater or Freshwater Aquariums, and Turtles - Auto Intelligent LED Digital Display by Brenda Perry

It's my fault but I used this 15w heater in 5.5G. It works fine, but the temperature in my tank tends to fluctuate quite a bit, so I woke up and the temp was around 75F (I wish it was closer to 80F) and it would last all day and it ended up being only about 78°F. He couldn't keep the temperature in the same spot. But if you use it for a smaller tank, you'll be fine!