I have an old heater that I used for my two previously owned snakes. It is a mat that sticks to the outside of the tank. I have a small two gallon tank and would like to know if this heater would benefit my sickly betta girl lily. It keeps the temperature around 80 degrees and since it was once for thier 50 gallon tank it covers more than half of one side of the small tank. If anything I suspect she will stay closer to that side of the tank. Should I use it?