All ponds will contain billions of minute bacteria. These include helpful species that Breakdown the toxic fish waste in the biological filter system, and convert it into nitrate, which is then taken up by the plants. However, there are also other bacteria that live in the pond that are opportunistic invaders of stressed and wounded fish, including the species Pseudomonas and Aeromonas which will infect any cut or abrasion on the surface of the fish, and can also invade the host across the gut wall during gastro-intestinal problems.
Acriflavin, when added to the pond, will reduce the numbers of these opportunistic bacteria in the pond, thus lowering not only the chance of infection, but also the intensity of disease in already infected ponds.
Acriflavin is ideal to use in hospital or quarantine tanks, but it is unwise to constantly add the treatment to the pond when the fish are healthy. This is because a background level of bacteria is essential for healthy fish to maintain their immune system.