HTH™ Shock 'n swim. Destroys organic contaminants. 1 balance. 2 sanitize. 3 shock. 4 prevent algae. Hth® and pH Plus® are registered trademarks of Arch Chemicals, Inc. The Hth™ logo is a trademark of Arch Chemicals, Inc. Helpline: 866-HTH-POOL. Toll-free. Call 7 days a week with your questions concerning pool water care. 8:00 A.M.-10:00 P.M. eastern time. Visit Hth Pools www.hthpools.com. In case of emergency call: 1-800-654-6911.