A nice aquisition Tony ! I had a Desjardin(Sp?) Tang that came with the used 90g I bought a few years ago. It died mysteriously a few months ago. It had severe lateral line erosion. Twenty fish in the tank, simple diet of flakes from original owner. Neither being a contributing factor though I'd say...
I was fortunate to see an awesome recovery though with a proper "herbivore" diet and a seriously reduced bio-load on the tank. Some "scarring" was permanant though.
Not an advocate of quarantine ? I agree to let "him" settle and see if the ich clears but it's good to have a hospital ready to use if things take a turn for the worse.
Yes, Cleaner Shrimp have gotten ridiculously expensive !