Hello! I just got a male adult BP (first snake pet) from a friend, I've been doing some research on how to properly setup his environment. Apparently the use of an under tank heaters along a thermostat is preferred to get the appropriate temperature and that's how I have it setup, however I can't get the temperature to reach 90 F on the warm side of the enclosure, it only goes up to 82 F. Here are some facts that may help find the problem:

1. The tank is a 55 gallon Tank, glass.
2. U.T.H used is Reptitherm heat pad - 40 Gallon terrarium size
3. U.T.H ocuppies about 25% of the bottom part of tank
4. Thermostat used is Zilla upto 500 watt and it is set to 91 F
5. U.T.H is connected to thermostat
6. Thermostat Power and Heat Source are both on
7. Thermostat probe is located inside and almost reaching the floor of the tank right above where the U.T.H is located
8. An additional thermometer is installed with its probe next to the thermostat probe
9. The tank top is covered with mesh cover
10. Substrate used is aspen and is about 1.5 inches height.
11. Cool side of tank never goes below 75 F
12. Humidity is 60%

Other than that I can say the snake has been eating well and at night time he goes out his hide (on the warm side) and seems to be active.

Any thoughts on how can I improve the enclosure temperature?? I'd like to stay away from heating sources like lighting since is my understanding these snakes are more nocturnal... Anyways I am not an expert and that's why I am asking for help. Thank you!!!