Bernice Brewster

Koi will flick and flash when something is irritating them. One of the reasons why Koi behave in this way can be due to poor water quality, most often due to the presence of nitrite, which is a skin irritant. Other chemicals dissolved in the water, such as chlorine, can also cause Koi to flick and flash. It is always worth eliminating water quality problems as the cause before pursuing any other course of action. Parasites, and occasionally bacterial skin infections, can also cause Koi to flick and flash. Those that cause irritation are visible to the naked eye, such as fish lice or even leeches, but there are also others, which are only visible under the microscope. If the irritation is due to poor water conditions, then regular, partial water changes are necessary until there is no nitrite left. Parasite infections can be treated using a proprietary medication, but be certain to follow the directions carefully and complete the course of treatment. If no parasites can be identified, but the Koi are still irritable, seek professional guidance.