In the past when fish developed disease in reef tanks, it was very difficult to properly treat the sick fish. Chemicals could be used to treat the infections, but were not safe for reef tanks with live rock, corals, and invertebrates. In order to treat the fish, the fish needed to be removed from the tank and treated in a separate holding tank. This process was not perfect, but did work. Moving a sick fish is very stressful, and makes survival that much more difficult. Time is also an issue. Depending on the disease it may take up to six weeks to ensure your fish and tank are free of disease.