The ich only lives on fish.... it will not live on inverts or coral. If you can keep your tank free of fish for about 6 weeks, all of the ich will die off because there are no fish for it to feed off of. that's really the only way you can rid your tank of ich... by keeping it fish-less for 6 weeks. Some will tell you that 4 weeks will do the job, but if I were you, I'd wait the extra two weeks just to be sure that ich is completely gone.
I know it kinda sucks to think that you can't keep any fish in there for 6 weeks, but it's actually a pretty awesome opportunity... a LOT of fish tanks have ich out there, especially in all the fish stores... they have no way of getting all the ich out of their tanks, so they usually feed them vitamins and garlic. Anyway, it's an awesome opportunity because this gives you the chance to completely rid your tank of ich. Most people have fish and find out they have ich, then they have to get a QT going and deal with all that Bullcrap, but because you don't have any fish, it's perfect.
Another thing though, if you add more fish, there is no guarantee that they are ich free. It would be good to do some kind of treatment on the fish you buy, like a chemical bath or something, before you put them into your tank. This can greatly help to keep the ich out of the tank. You'll hear from a lot of people that you should do a QT and keep it set up and all, but I know there are like 5 minute chemical dips and baths you can use to kill all the ich before you put them into your tank.