Sera aquarium heater thermostats are high quality products that feature shock resistant quartz glass, precision protection circuit and a protective guard. These heater thermostats are very short and are easy to install, especially in small aquariums. There are 6 heaters in the range, suitable for aquariums from 20 to 300 litres. This 300w model is suitable for aquariums from 150-300 litres.. Sera aquarium heater thermostats are very short and are easy to install in small aquariums. The function control on off is achieved by means of a small lamp.