Treating a sick fish can be difficult but rewarding.  It is handy to have a small quarantine tank present to treat individual or groups of fish. This is not only cost effective but allows you to monitor the fish without having it hide from view.   In the case of treatment with copper the main tank should not be treated if it contains corals or invertebrates as both are sensitive to this treatment.  Treatment with garlic is a popular alternative to copper however it has not been documented to be a total success.