Chlorine breaks down over time due to sunlight and other factors and has to be replaced in the pool.
I don't understand this.
Chlorine is a basic element, CL, number 17 on the periodic table of elements. Molecules composed of basic elements break down into the individual elements, but the individual elements, such as CL, only break down during nuclear fission, if I remember correctly from science classes years ago.
What is really happening to the CL in the pool water?