With a UV-system and a UV clarifier, you are well prepared for most of the fish diseases. With a UV-system, the tank water is channeled via a pump to a UV-lamp which kills the bacteria and floating algae contained in the water. It sterilizes the water and should always be in continuous operation. If it is not operated continuously, a UV-clarifier can be connected before introducing new fishes (especially delicate fishes which stoops even by a dot e.g. White-throated surgeonfish Acanthurus leucosternon) and then should run for a few weeks. A UV-system can also be used in bacteria blooms or algae blooms.