Clorox Pool & Spa Shock XtraBlue is a fast-dissolving swimming pool shock that kills pool algae and bacteria. It also removes swimmer contaminants. It will not bleach your liner or affect your water??s pH level like other brands. Shock your pool weekly and after pool parties and severe weather to remove contaminants, destroy odors, and keep water clear. No premixing required ?C just apply according to label directions. For best results, add to the deepest end of the pool with the filter running. Circulating pool water when applying chemicals helps disperse chemicals throughout the pool for maximum coverage. The best pool shock on the market, use once a week during your weekly maintenance program. Pair with the Clorox Pool app and XtraBlue Chlorinating Tablets for best results.