RENU Therapy has a 4-Part Purification System that is All Natural with No Chemicals required! Ozone, or energetic oxygen, is a powerful oxidizer, combined with a 10" Filter System, surface Dirt and Oil Remover Buoy, and a Spa Sanitizer Mineral Stick that uses silver ions to destroy bacteria and algae. The RENU Plunge Tank stays clean and rarely requires a water change which conserves water. Others require chemicals and or continuous water changes.