We bought this for our betta's 2 gallon tank. Even though you can't adjust the heat settings, it heats the tank just right to make our fish friend happy! My hubby made the mistake of leaving the heater on while it was out of the water (and on a paper towel =/) one time, which ruined the heater obviously. But we turned right back around and got another one! We've had this second one for a year and it's still doing awesome!