Pristine Extra (25 lb)Description Pristine Blue Extra is a chlorine shock specifically designed for the Pristine Blue Chemicals. It is typically added every other week, but can be added more frequently based on your bather load or if your water requires additional shock treatment. Alternatively, you can opt for Pristine Power (a non chlorine shock) to shock your Pristine Blue water. With 99% Sodium Di Chlor as its primary ingredient, Pristine Extra for pools is an