Marina Betta Heater is an automatic, submersible heater that creates ideal water conditions for bettas to thrive in. The exterior is made of durable polymer, which is more resilient than traditional glass sleeve heaters. The heater is designed to reach and maintain a set temperatureno manual adjustments required. It has a red indicator light that illuminates when the heater is working. It comes with a suction cup, so you can easily install it against the aquarium window. For aquariums up to 5 litres