Fish diseases and parasites can pop up almost from out of nowhere, with no readily apparent cause. When this happens, the best approach is to remove all of the afflicted fish from the display aquarium and place them into a quarantine/hospital aquarium until the fish get completely healed. This will hopefully remove the parasite or disease from the tank, but if it doesn’t, it will at the very least reduce it’s presence. The quarantine/hospital aquarium doesn’t have to be an elaborate setup. Instead, the simpler the better. No sand is needed, but you also don’t want to use carbon as it will absorb any medicine introduced to the aquarium. The water parameters in these tanks can get out of hand very quickly, so it’s a good idea to constantly test ammonia and nitrite, as well as perform frequent water changes.