Tang... White spots on fin

[Metrontech]

Hey guys, hoping to get some clarity

Bought a yellowed eyed kole tang around 4-6 weeks ago

Since at one he has had white spots on his fins. After the first week it was evident that he had ich as it was all over his body

So I put him in the hospital and treated him. He sat in a hiding spot 90% of the day. The spots went away and he was returned only to find the spots the next day but only on his bottom to fins

It's been like this for a while now.

He eats and picks rocks all day

What do I do?

I have lps, softies and 4 other fish (who are all fine)

Any help would be appreciated