Zoo Med Bettatherm is a convenient small round size heater that is completely submersible for your Betta bowl. It increases water temperatures by 5-10 degrees Fahrenheit over ambient room temperature, keeping your fish warm and active! Zoo Med Bettatherm may be used in 1 to 3 gallon tanks and bowls made of glass/acrylic. 3" in diameter; 7.5 watts.