If you’ve tried it all and nothing works, AND YOU’RE ALSO A LONG TERM USER OF STABILISED CHLORINE, you’ve probably got ‘Chlorine Lock’ or ‘Over Stabilisation’.
Why? Pool Stabiliser (a.k.a. ‘Cyanuric Acid’) works by holding on to chlorine to prevent it from being dissipated by the sunlight (UV). But concentrations build up until it interferes with disinfection. Too high and chlorine gets ‘Locked Down’ till it stops disinfecting. THIS OCCURS LONG BEFORE THE WATER GOES GREEN! So remember: clear blue water does NOT mean a Hygienic pool!
THE BAD NEWS: Cyanurate concentration can only be diluted by draining the pool (30% – 50%) and topping up with fresh water.