One of the more common ailments of Koi and Goldfish in the pond is a fungal infection. This is a very opportunistic disease and usually starts with a small scrape or possibly an open bacterial wound on the fish. The fungal infection generally first attacks the dead tissue of a wound and can then spread to healthy tissue, especially on the gills and fins of the fish. While not immediately deadly, if left untreated the fungal infection will result in the death of the pond fish.
Most treatments for fungal infections are liquid “water bath” solutions added to the pond daily/weekly during treatment. Since the fungus is often associated with a secondary bacterial infection, most anti-fungus treatments will also fight bacterial diseases. The treatments can be plant based natural products or chemical treatments known to kill the fungus without harming the fish.