well if you use a thermostat that the heat mat plugs into you can adjust/regulate the temp,
otherwise the heat mat will just stay on all the time witch is a good thing IMO.
FYI. only if you did not know this already: do not put the heat mat on the bottom of the tank, put it on the back side of the tank...
i hope this helps.
? are you going to use a false bottom set up ?