Clorox Pool & Spa XtraBlue 3-inch Chlorinating Tablets are multi-functional swimming pool chlorine tablets work that kill harmful bacteria and unsightly algae. Each tablet dissolves slowly and contains stabilizer for a long lasting clean. The XtraBlue Formula protects your surfaces from scale and corrosion and has conditioners that make your swimming pool water feel silky smooth. Use weekly in skimmers, feeders or floaters. Always apply chemicals per label directions. The best time to apply these pool tablets is when you test your water each week with the Clorox Pool app. Since it gives a personalized recommendation for what your pool needs, there's no guesswork involved. Simply enter your test results or scan a Multi-Use Smart Strip.