The gills are probably infected with ich, remove fiish and treat not only with the copper but I suggest Furan2 for the infected eye. Do not attempt to feed during treatment. Remember copper or formalin does nothing for the fish when the parasite is on the body. These drugs only kill during the free swimming tomite stage. The hyposalinity helps relieve the trophont stage when it's on the fish. The tomont stage is the dormant one.