Granular chlorine is a type of dry chlorine that is primarily used in cleaning swimming pools. It is also known as calcium hypochlorite. It is one of the two forms of solid chlorine, the other being chlorine tablets.
The granular chlorine is used once a week to shock the pool or once a day as a daily dose of sanitizer. A pool shock involves raising the level of chlorine in the water so high that it kills bacteria and neutralizes organic material. The amount you will need depends on the amount of water contained in your pool.