Trust me... Even us old ppl <namely me> have a lot of questions and issues. Main thing is that you are seeking answers.

If your humidity is accurate at 59, that is fine for shedding, balancing your temps may drop it a little, ideal is 50-55 ish. Temperatures.... 70-85 is a pretty big difference in a 20L. Is he staying on the hot side? If your room is cold, close the ac vent a little to raise the temp? Make sure it's not blowing right on the tank.

You didnt answer the thermostat question... You really need one if you are using an under tank heating pad. That and an infared temperature gun will be your new besties.