Sustain ¾-inch blue, Shield Energizer Tablets make the shocking process simple, quick and effective. Every time you use Shield Energizer Tablets, you replenish your Summer Shield reserve bank of chlorine protection. Use the measuring cup that comes inside each package to fill your skimmer basket with the required amount of tablets for your pool size (see package label directions.) These shock tablets are designed for use with Sustain Summer Shield Chlorine Extender and Sustain 3” General Chlorinating Tablets.