I added a sailfin to my main today and the purple tang started pestering him. Just constantly pushing against him.
I had the same issue with a Purple Tang. Many people at the LFS
told me that we could put him in there and it wouldn't be a problem, but he attacked my tangs, 1 in particular, pecking at his fins until he was so stressed out that he had red spots all over him.
I took out the Purple Tang and returned him the next day. I did some research online and found out that Purple Tangs are aggressive and are not to be put with tangs of the same body shape.
It's a shame because I absolutely LOVE the Purple Tang, but it's not worth my other 4 Tangs.
At any rate, I don't think putting him in isolation will work. I think it will only stress him out even more and you may loose him. If there's not alot of places for the Sailfin to hide, you may be in trouble with this combo of fish.