Help with temps for my snakes?

I have my to big snakes (the BP and the CA King) in sterilite tubs (110 QT). I have a zoo med UTH for both of them, but the tubs just won't go to the right temps. Its about 78 degrees in my house and its 79 in the tubs. I need the heat to go to about 82-83 for both of them. But the UTH's won't do it. And the pads are brand new.

But, the snakes are healthy, and are eating. I just want the right temps. Any suggestions? Thanks.

What are you measuring the temps with? are you using a thermostat or dimmer on the heat pads?