Review on IOAOI 50W Aquarium Heater for up to 20 Gallon Tanks - Shatterproof, Suitable for Marine and Fresh Water - Engineering Plastic Tube & Stainless Steel Inside - Adjustable Temperature by Kimberley Cook

At first I only bought one for my 5 gallon betta tank but it worked and I bought another for my 20 gallon guppy tank. Now I'm buying a third to heat water when I do water changes as a backup if I ever need it. I was attracted to this heater because it was black and not glass so I didn't have to worry about it exploding. I still disconnect it when doing a major water change that causes the waterline to drop below the minimum waterline printed on the unit. The device runs a little colder than I expected. It's preset at 78 degrees Fahrenheit, and according to the thermometer in both of my tanks, the water temperature is usually between 74 and 77. The temperature dial is a little hard to turn, but that might be a plus and not a minus because I don't know. I don't have to worry about snails or fish accidentally turning the Nob over while it's in the water.