Aqueon Adjustable PRO Aquarium Heater Up to 20 Gallons, 50 Watts

The Aqueon Adjustable Pro Aquarium Heater is a reliable and effective product, though there have been mixed reviews. The thermostat is unlikely to fail, but in the unlikely case that it does, the heater can cause harm to the fish. Therefore, using two smaller heaters or choosing a lower wattage option is recommended for an added layer of safety. The heater is fully submersible and has an adjustable temperature dial. It cycles on and off to maintain the set temperature and the user can see the light turning on and off. The 300W model does not have a green light, but the red light indicates that it is operational. It is suitable for aquariums up to 20 gallons, although it takes a while to bring larger tanks to temperature, according to one user. The heater needs to be fully submerged and should be mounted vertically or horizontally. The temperature calibration of the unit can sometimes be off and may require some adjustment, though sometimes the unit does not work at all. The suction mount may be less effective than it could be. The metal outer tube makes it longer-lasting and less prone to cracking and leaking than other brands.