- Pool chlorine comes in a gas, liquid, granular and tablet form. Liquid and gas chlorine are unstable forms of chlorine, but tablets and granules are stable and recommended for pool water care. With tablets and granules, it is easier to maintain chlorine readings in the pool between 2.0 and 3.0 parts per million (ppm).
- Pools have free chlorine, which is chlorine that has not been affected by or reacted to the substances in the pool water. The ideal reading for free chlorine is 1 to 3 ppm.
- Combined chlorine is the chlorine in the pool that has had some reaction to substances in the pool water and is no longer considered free chlorine. Combined chlorine readings should be kept below 0.2 ppm.
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