Get a 12" net, leave it in the tank so he gets use to it, and bait him with nori up against the wall. When he goes in to eat, BLIKITY-BLAM! Then get that guy in QT. I found that a 36" tank, even if it's not a tall one, seems to work best for tang QT's.
I researched UV a while back, and for a system of your size, the rate you have to pass water through to even remotely impact ICH, and the amount of dwell time it requires... You're probably talking a grand plus for a solution, and even at that it's no guarantee what so ever.