Our chlorine granules are manufactured with a stabilising agent to help prevent the destabilisation and destruction of the chlorine by sunlight and UV rays. This prolongs their usefulness as a sanitiser over other types of non-stabilised chlorine and makes them ideal for use in swimming pools, spas and hot tubs whether located indoor or outdoor. These chlorine granules should be routinely used to help maintain a safe bathing environment. Swimming Pools: Routinely use between 2-3ppm residual chlorine in small or domestic pools and 3-5ppm in public or heavily used pools. For each ppm of chlorine increase required use 40g per 25,000 Litres of water. Spas and Hot Tubs: To increase the free chlorine level by 2.5ppm, add 5 grams (a teaspoon). On average you should need approx. 1 teaspoon per person using the spa. Maintain a chlorine level of between 2-4ppm and a pH level of 7.2-7.6 in your spa. Re-adjust the pH balance to between 7.2-7.6 for optimum bathing comfort.