Review on 🐠 FREESEA Adjustable Thermostat Aquarium Fish Tank Heater: 50W, 100W, 300W with 2 Suction Cups & Thermometer - Ideal for Betta Tank, Saltwater Tank, Aquariums, Coral Tanks by Michelle Dreger

I have this heater in an 8.5 gallon tank. Ambient temperature 68°. The tanks sit on a granite countertop. As long as the heater is on I can't say it works too well. First, when you get the heater, ignore the temperature controller at the top. It's absolutely useless. If I set it to 78° my tank would be 85°+. Even after I set the cut-off temperature to 78, the temperature fluctuates between 72° and 78°, which makes me a little uncomfortable. I do not recommend this if you are keeping fish with sensitive temperature requirements. From the looks of it, that 6 degree window is barely enough for the few guppies, tetras, shrimp, and plants I have. I'll probably put in a replacement thermostat to more precisely control the temperature.