Removing the Ich from the fish only kills the adult trophont stage. Ich's lifecycle includes stages that live in the sand bed and in the water.
you cannot only treat a fish for ich, you have to treat the fish and its tank.
You can either remove all fish and treat in a quarantine tank letting the display tank run fallow for 4-6 weeks, or you can treat the display tank, (copper or hypo). Obviously either technique will kill inverts and corals.
If you only take the Ich off of the fish, it will come back in a few weeks or months.
Fish can develop an immunity, so repeated dips over a prolonged period may help a fish to cope with the nuissance, but the ich will still be present, waiting to prey on any fish whose system can't handle the infestation.
Josh