Terta Fish Tank Submersible 2-10 Gallon Aquarium Heater With Self-Adjusting Thermostat - Featuring A Compact Design and Submersible Technology, The Whisper 2-10 Heater Makes Heating Small Aquariums Easier and More Affordable Than Ever. Just Submerge Heater In The Aquarium and Plug It Into An Outlet. There's No Thermostat to Set, So There's No Hassle About Temperature Control.