GreenClean Granular Algaecide - 2.5 lbs - String Algae Control for Koi Pond, Fountain, Waterfall, Water Features on Contact Treats up to 5,000 gallons. Non-harmful to fish and aquatic plants when used as directed. Alternative to harsh chemicals  Chlorine, copper and phosphate-free. Begins working on contact, killing algae fast; results in 24 to 48 hours. Immediately begins fighting algae blooms, releasing vital oxygen into the water body as it biodegrades.