As I mentioned in my PM my PBT had one outbreak of ich early on. I believe it was caused by a heater malfunction that allowed the temp to drop. Since I had just transferred to the 90g a month earlier I was not taking it apart to catch the fish.
I started using garlic extreme as a food suplement and daily added 1 drop per 10 gallons. I know garlic is not supposed to be a treatment, but in my case it worked. No other fish came down with ich. Sometimes I think in our interest to have perfect fish our cures can be just as stressful as the ailment.
BTW, I had the tang for another 9 months after that until it mysteriously died while I was out of town.
If you are willing to risk it I say leave it in the main and treat with garlic. Watch for other inhabitants that may be stressing it as well.