Chlorine stabilizer is used, in outdoor chlorine-maintained swimming pools, as a means of helping to protect the chlorine from being destroyed by the Sun's ultra-violet rays. This helps the chlorine last longer and reduces consumption. The level of stabilizer is easily determined by a simple chemical test, with a range of 20-50 PPM being ideal. Higher levels, especially over 150 PPM, are thought to reduce the effectiveness of the chlorine and may require the maintenance of somewhat higher chlorine levels. Every time stabilized chlorine is added, some stabilizer is contributed to the water. The only means of lowering the stabilizer level is to replace water
