Free chlorine is the chlorine level that you test for in your pool and is ‘free’ to do its job and sanitise the water in your pool. It is essential to know how much free chlorine is in your pool, when compared to combined chlorine, which has already been used up in the sanitising process, although it is still present in the water. Free chlorine is what is needed to protect your pool. A pH imbalance, suspended dirt or extreme stabiliser levels can reduce the accessibility of free chlorine. The right level of free chlorine in a swimming pool is between 1 and 3 parts per million (ppm).