All fish do not have ich, nor do all tanks. It's possible to have an ich free system as long as you rigorously quarantine everything (and I do mean everything) before it goes in your tank. I'm currently running 6 tanks, none have ich. Water changes don't get rid of it, cleaner shrimp/fish don't either. The only way to kill it is to deprive it of a host (fish).
Since your tank is fishless, leave it without fish for a minimum of eight weeks. The ich must have a fish host in order to live, no fish=no ich. And quarantine everything new before you put it in your tank. There are a lot of very good articles out there about ich, the life cycle of the parasite, and how to get rid of it forever. And there is no reef safe medication to eliminate it from a reef tank. Kick ich, Rid ich and the like are all snake oil. The truly effective treatments must be used in a bare hospital tank.....copper, quinine sulfate, hyposalinity treatments, all effective, and none can be done in a reef.