So... What now?

[DKoKoMan]

Trial and error (sucks I know) but I would monitor the tank. From the sound of it I think It was isolated to the new Kole Tang. I'm with you on not wanting to isolate the fish and begin treatment unless absolutely necessary.

[intarsiabox]

Unfortunately ich will remain in the tank forever as long as there are hosts. It doesn't effect most healthy fish that are established and you may never see the signs of ich again with your current occupants. It's a tough call but at this point I think you will be worrying every time you add a new fish to the tank. As a side note my shrimp always get just as much attention from people, if not more, than my fish and don't get ich. Good luck!