You should remove the tape from the probe, tape inside the cage is a tragedy just waiting to happen. Hot glue can be used to secure probe inside the cage, just use as little as possible so you don't insulate them.

You really don't want the cage to be any cooler than 75 degrees.

Do you have any sort of light for the tank? A low wattage fluorescent or even something like a 50 watt infrared heat lamp will fix your cools side/air temperature problem.