Yeah, I give up. It hasn't budged from HI since I turned it on and put it in. My old model is showing 75% humidity. When I pulled away some of the foil on the screen it went down to 72%. Their temps are comparable. So I think this particular model simply sucks at humidity although is accurate at temp. Perhaps next month when it comes time to tear down the tank I will look to reinstall my old model. Maybe I'll email the company.
On the plus side, the insulation that I lined the outside of the tank with, and the foil on the screen seems to be doing well to keep temps consistent and seem to avoid the dissipation of humidity a bit.
And just a note, there is not and was not any condensation. So I guess that's a good thing.