I am unsure of how to treat this guy, because I am not sure of root cause of him looking like this! i have had the tank for over a year now, in that year i never vacuumed the gavel, only did water changes. he was living in cold water with 3 goldfish and one koi fish. i took out the koi and goldfish and got another smaller koi. my mom brought home 5 koi fish from the pet store, they did not get quarantined . my mom just put them in there. Anyway they all got ich, i was a little delayed getting them treated because i had to find the right treatment. but anyway a month later now he is like this. I have a heater, two filters and a air stone. he has now two small kois in there with him. what does it look like to you?