Applied Biochemists Resist is a unique treatment that effectively neutralizes the minerals dissolved in your pool water, preventing ugly metal stains as well as scale buildup. This long-lasting sequestering formula prevents damage to equipment and pool surfaces typically caused by stain and scale, and should be added anytime freshwater is added to your pool, such as during initial filling. Best of all, Resist doesn't require you to shut your pool down after treatment, allowing swimmers immediate access!