Well Ich has a life cycle of 30 days so to kill them all you'd have to deprive them of a host for the entire life cycle. (you never know where they're at in the life cycle) Almost impossible without removing fish from the tank.
We can only see ich for one week of this cycle if memory serves me correctly.
If I were you I'd QT the fish for no less than 30 days and to be safe I'd do it for more like 45 days.
If the meds you're using contain copper don't put any more in the tank. Might want to get some copper sponges if that's the case...