Norweco Blue Crystal Residential Disinfecting Tablets 10lb - Septic Tank Chlorine Tablets Specifically formulated for residential wastewater treatment systems Maintains disinfection in low and intermittent flows Promotes a stable pH level U.S.E.P.A. approved for wastewater treatment Designed to provide rapid disinfection, the potent formulation of Blue Crystal reduces 99% of bacteria within the first ten minutes of contact