thanks for all the feedback. I agree that QT should not be a stressful place, and don't think the fish was stressed by QT. Rather, just terrified of humans entering the room. I would sneak and glance around the corner to see him swimming happily around, but once I enter the room (even at a snail's pace) he would immediately swim to shelter and stay there until I had left. That is why I decided to move him into the display once he was showing signs of possibly starting to eat. In hindsight, I don't think I'll ever move another fish until it starts eating, etc... so lesson learned there.
I find tangs to be quite twitchy in QT. Adding lots of PVC helps, but they all seem to run for cover (except my current Naso who behaves a bit more lik a dog than a fish).