The very word can strike fear into any marine aquarist. Diseases, particularly ‘velvet’ and ‘white spot’ are real threats.
The threat can be minimized of course. Careful selection of fish is the initial way, being careful to ensure the selected ones are as ‘clean’ as they should be. Other intended livestock should also be carefully inspected.
A second line of defence is the quarantine tank where any disease can be treated and cured before it is introduced to the main display aquarium where it creates a threat to other livestock. Strangely, most marine aquarists do not make use of quarantine instead introducing their livestock direct. This is taking a chance as dealing with disease especially in a reef system could be difficult – difficult because copper, the number one treatment for certain diseases, is deadly to corals.
The question of disease and its treatment is wide and quite varied. Most marine books have a section on disease which can be of assistance.
Here are two videos which deal with the subject, they are good quality and actions are clearly explained. A large part of the videos deals with cleaning up the aquarium prior to medication. Obviously the instructions on the medication container must be properly followed relative to the net gallonage of the aquarium. Finally, as already mentioned copper should not be used in a reef system – if there is any doubt check the medication manufacturer’s instructions and suggestions.