API Marine Stress Zyme is all natural, live beneficial bacteria for cleaning marine and reef aquariums. Keeps live rock, coral, sand, gravel and glass clean. The zyme contains millions of live bacteria to consume sludge and organic debris to reduce aquarium maintenance, while improving water quality. Features: Contains millions of live bacteria Used For: Aquariums Health Consideration: Keeps aquarium clean and easy to maintain Weight: 16 oz Caution: Keep from freezing. Do not store above 120F. Keep out of reach of children. Directions: Use weekly for a healthy, clean aquarium and to maintain a strong biological filter. Shake well. Use dosing cap on bottle. To maintain a clean, healthy aquarium: add 5 ml per 10 U.S. gallons of water weekly. For new aquariums, when adding live rock, to help boost the biological filter: Double the dose, use at start up, and for 2 additional weeks.