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Leisure time chemicalsThe purpose of the Reserve (bromide). After you get out of the water and shock it with Renew. It generates the bromine then after the bromine does its job it is gone. You wont get a reading after a few hours. However you will still have a bromine reserve in the water it just wont show up on the test strips. They made this product because so many people were interested in a bromine or chlorine free system. With Reserve you still have the benefit of bromine to sanitize but when you get in the spa it is essentially bromine free and completely sanitized. Jackson