Aquatop's TH-C series of fully submersible titanium heaters with controller offers a compact design for versatile placement and are extremely durable thanks to the tough titanium heating element construct. Temperature range is 68F - 92F, and each unit has a separate temperature probe to help ensure even temperature readings.
I would definitely recommend adding these little guys to your tank. They are very playful and entertaining. My three were very healthy and quickly adjusted to my tank.