What are your temps at that you need to get them up?

A 55 gallon tank is going to be very hard to heat. If you can't switch to a smaller tank, you could try covering the sides and most of the top with rigid insulation to keep the heat in.

I'm not sure what you're using for heat pads, but they shouldn't be "in" the tank ... that could be a major fire hazard with the water dish in there.

-adam