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.  At closing time, Sustain Shock can be used in conjunction with Winter Shield.  (Always apply shock to water, not water to shock!)