If you're using an under tank heater then you need a thermostat for it. I like the hydrofarm. It's cheap and it works fine.

I have the SAME exact heater you have. It heats through my aquarium glass to 112F without a thermostat. YIKES!

If you provide an ambient temp of 81F with a hotspot of 90-92F you should be just fine. 81 is a good ambient temp, but you need a regulated hot area.

I have a hard time believing that you are getting 70% humidity on aspen. If so, move your water dish to the coldest corner of the tub.