Chlorine, which we use as a sanitizer in our pools, is very unstable. The effects of the sun's UV rays and high temperatures reduces chlorine's effectiveness and breaks it down into inactive components.
Stabilizer, or cyanuric acid, is a compound which protects the chlorine from the negative effects of UV and heat. It not only ensures that our pool remains clean and safe for the swimmers throughout the day, but it also reduces the amount of chlorine we need to add in order to maintain these levels of disinfection.
"According to research results, pools without stabilizer lose about 90% of their total chlorine residual on a sunny day in two or three hours. Pools treated with 25 to 50 milligrams per liter of cyanuric acid, however, under the same conditions, lose only 10 to 15 percent of their total chlorine." (White et. al. , 1972)
Ideally, the stabilizer should be maintained at a level of about 50 ppm, the acceptable limits being 40-80 ppm. The chlorine tablets have stabilizer in them, over time this increases the amount in the pool. If the stabilizer becomes too high, it makes the chlorine ineffective as a sanitizing agent.
To reduce the amount of stabilizer in a swimming the recommendation is to drain and refill the pool.