June to September: when chlorine cannot keep up
Summer chemistry is a losing race that you manage rather than win. Ultraviolet light destroys free chlorine, and hot water accelerates every reaction, so a dose that held for days in January can be gone within a day in July. The standard defence is cyanuric acid, the stabiliser that shields chlorine from sunlight, but the UAE has a particular trap here: trichlor tablets add stabiliser with every tablet, and by late summer many villa pools are so over-stabilised that the chlorine reading looks fine while the water is barely sanitised. A competent technician tests cyanuric acid monthly in summer and dilutes with fresh water when it creeps too high.
Evaporation is the other silent load. Losing five millimetres or more a day does not just lower the waterline; it concentrates everything left behind, so calcium hardness and total dissolved solids climb steadily through the season. That is why summer top-ups matter and why an autumn partial drain-and-refill is normal practice here, not a sign of neglect.