The Natural Alternative to Chlorine (and Bromine too!) Product Features: Lasts four months. Makes spas easy to manage. Improves performance of ozone-equipped spas. Assures an odor-free spa. Significantly improves look & feel of water. Simplifies water balance - it's unaffected by heat. Specifications: Capacity: for spas up to 500 gallons. Run time: minimum 4 hours daily. Flow rate: works with all spa flow rates Installation: Drops into the core of most spa filters works with suction-side and pressure-side filters.