Sustain® W8000211 24 lb Pail Calcium Hypochlorite Shock Treatment, contains 1 lb pouches. Sustain® Shock Treatment is a powerful and quick dissolving oxidizing product used to eliminate algae, bacteria and germs for pool water. It is also an excellent preventative to help these problems from developing. Sustain® Shock is an ideal product to use at the very beginning of the season to establish a chlorine residual in your pool before startup of the 3-part system. It can also be used during the summer for a quick shot of chlorine when water appears dull.