Review on 🐠 Aquatop Nano Aquarium Heater 15-Watt - Perfect for 2.6 to 4 Gallon Aquariums at 77°F! by Jami Boetel

If you expose the reactor core, you have Chinese Syndrome. In other words, keep it submerged or it will likely fail like mine. I had a 5 gallon top fin with a built in filter on the back. The filter is clogged and the water level in the rear filter where the heater was stored has dropped. Heating out of order. There is a water line gauge on the heater and it's probably not the fault that it went out. It kept the water at 77F so it did the job well, maybe too well as I prefer 74 degrees for my tropics, they seem just as happy and eating less. In addition, the colder the water temperature, the higher the oxygen content. I will buy it again if I need it again I would definitely consider buying it again but I would install it in the main tank area but that would leave an ugly wire you would see.