Granular Chlorine is used as a sanitiser for spa water. Please ensure to follow the chemical instructions for this product.

Use a bucket and scoop some of the spas water into the bucket until it is roughly ¾ full, then add the granular chlorine to the bucket of water and stir (avoid contact with your skin), after 60 seconds pour the water from the bucket into the spa and run jet 1 for 5 minutes.
Do not put any of the chlorine granules left in the bucket into the spa they need to be thrown out.