Review on Hygger 200W Digital Quartz Aquarium Heater with External LED Display - Auto Submersible Heater for 15-30 Gallon Fish Tanks by Tyler Jacob

This will raise the temperature fairly quickly and keep it stable. In the winter I keep our thermostat on 65 but the fish are toasty warm. The only problem I have is that the suction cup used to hold the digital display doesn't stay on for more than an hour or two. The internal suction cups have been in use for over a month now and are holding steady. It's easy to set up and use. I recommend this heater