I have 2 tinfoil barbs, 2 jack dempseys 2 upside down cats and a priscilla. most of the fish have been scratching themselves on the gravel for the past week and I just now noticed a 'white cotton ball' on one of the barbs' lips. Im guessing this is a fungus but its been YEARS since ive dealt with fish illness so.... whats my best course of action?