OK, here are my suggestions - and yes, I've had a PBT for over a year:
Quarantine him in a bare-bottomed tank, as big as you have - I'd use the 45. You can set one up by taking some live rock and water from your existing tank.
A UV sterilizer can't hurt, but if you don't have one, I'm not sure it's necessary. You will likely go thru at least 1 cycle of Ich. Give him/her plenty of hiding places to sleep at night. Feed it often and well, with nori or some other greens available all or most of the time. If you have a supply of live brine or saltwater ghost shrimp, I'd try those as beginning foods. What you want to do is have him/her in the least stressful environment you can, with good water and a full belly. Keep it in the QT until it has been Ich-free for 3-4 weeks. When you introduce it into the big tank, rearrange some rock to put the other fish off-guard.
Bill
215g FOWLR... and anemones, GSP, gorgonians... carp, that isn't FO!
"I killed my first SW Fish in 1971..."