Personally, I don't treat ich unless the fish is in a QT before it heads to the display tank. If it gets in the display then it's on its own. I am sure to feed a high quality diet with vitamin drops and garlic. I haven't had an ich outbreak since...hmm, since under gravel filters were the in thing.
In your case, if you're insistent on treating it I would use hyposalinity (you need a refractometer to do this) instead of medication. Many medications actually cause permanent damage to a fish's immune system, and god only knows what else. In your case, I would move as much rock out as possible (since hypo will damage the nitrifying bacteria) into a container with a heater and powerhead (it's fine with no light...will lose coralline, but it comes back fast), then use hypo on the tank with the remaining rock. I wouldn't worry about the rock containing more ich since ich can't attack unless the fish is stressed or otherwise compromised. Plus, if you ever add another wet thing (rock, coral, fish, inverts, etc) to that tank you will be reintroducing ich anyway, so who cares? Most if not "all" tanks have ich present, it just isn't attacking the fish.