Sorry for the scatterbrained abundance of posts, I don't know how to edit my previous posts lol- but anyway, putting the probe between the bottom of the tank and the UTH helped DRAMATICALLY. Wow. It's coming up to temperature right now. I think his tank was colder than I thought it was, and that was probably why he was refusing and such a bad eater in the first place. I've added insulation on the back of his tank and one of the sides with the leftover foam I already had. Hopefully the temperature issue will resolve itself now that adjustments have been made. So glad I made this post.
Awesome to hear and I'm glad you were open to everyone's advice! Make sure you take several temperature readings to make sure you have it where it needs to be.