Your swimming pool water must be COLOURLESS, TRANSPARENT, VISUALLY and BIOLOGICALLY CLEAN, For water maintenance, add only chlorine in order to keep the free-chlorine content at between 1 and 2 ppm. Free-chlorine must be controlled periodically with the aid of the test-kit. Check that the controls show the “correct zone” if not, “correct” it. Frequency of controls must be increased in the case of special circumstances, i.e. very hot days, storms, large numbers of swimmers (sweat, tanning creams, etc.), dust pollution, leaves, flower pollen, etc.