Prazi Quantal 50 gram size. Excellent fluke worm treatment and dewormer. Great for Koi. Safe more most freshwater fish. Treats 5,000 gallons Easy to use. This is a special order item only with a 2-3 day lead time. Prazi is extremely effective for the treatment of external flukes, liver flukes, internal parasites and internal worms in koi, goldfish and tropical fish. Prazi is a one time treatment and because it is so gentle, it does NOT require any water changes after treatment and you do NOT need to bypass your biofilter. Prazi also will work with any amount of salt in the pond and it is not water temperature dependant.