Dimilin 25W powder is by far the best treatment for fish lice and anchor worms in Koi and Goldfish! I normally treat at a dose rate of one gram of Dimilin per 264 gallons on pond/tank water for four days. Then do a 25%-50% water change when complete. Usually only one treatment will do the job, but sometimes a second treatment one week later is called for for heavy infestations of lice and anchor worms. Comes with complete dosing and application instructions.