there is no cure for ick, it is always there, it gets on fish due to them being stressed. Ick cannot be removed. You have to wait until it finishes it's cycle of reproduction in order to kill it. Sometimes chemicals can actually stress the fish more and cause ick to get worse. low salinity and high temperatures cause ick to hastefully finish it's cycle and mroe comonly finish prematurely. At the end of the cycle it falls off but comonly gets right back on the same fish and starts over. Copper kill it before it can get back on but not while it is on. You may wish to try no chemicals, and then put the fish back in the aquarium and treat the empty QT tank after all parasites have fallen off. The more prestine the water is, the less tressed the fish will be and parasites may not get back on him at all. On top of that, your cleaner shrimp may supply a valuable servicee to him in this state.