Pool Chemistry in UAE Heat: The Five Numbers That Actually Matter

Most green-pool emergencies in the UAE are not caused by too little chlorine. They are caused by chlorine that cannot work, because one of four other readings is wrong. Understanding five numbers is the difference between a pool that stays clear all summer and one that needs a costly recovery every few months.

1. Free chlorine: 1–3 ppm (aim for 3 in summer)

This is the chlorine actually available to sanitise. UV and heat destroy it fast here — an unstabilised pool can lose most of its free chlorine in a single sunny day. Test it at least twice a week from May to September, and remember that "I added chlorine" is not the same as "the pool has chlorine": if the reading is zero hours after dosing, something else on this list is wrong.

2. pH: 7.2–7.6 — the number that decides everything else

This is the reading most owners ignore, and it quietly controls chlorine effectiveness. At pH 7.2 chlorine is roughly 60% effective; at pH 8.0 it drops to around 20%. So a pool with "plenty of chlorine" and high pH is effectively unsanitised — which is exactly how pools turn green while the owner insists they have been dosing. UAE tap water and evaporation both push pH upward, so it needs regular correction downward with acid.

3. Cyanuric acid (stabiliser): 30–50 ppm

Stabiliser is chlorine’s sunscreen — without it, UV destroys free chlorine within hours in Gulf sunlight. Too little and you are burning money on chlorine that evaporates by noon. Too much (above roughly 80 ppm, which happens when using stabilised tablets exclusively for months) and it locks chlorine up so it cannot sanitise, a condition called chlorine lock that only dilution fixes. This single reading explains most "I add chlorine and nothing happens" cases.

4. Total alkalinity: 80–120 ppm

Alkalinity buffers pH — it stops your pH swinging wildly with every dose and every rain shower. Low alkalinity means pH bounces uncontrollably; high alkalinity makes pH stubborn and drives cloudiness and scale. Correct alkalinity first, then pH: doing it the other way round means chasing your own tail.

5. Calcium hardness: 200–400 ppm

UAE fill water is hard, so calcium climbs through evaporation over a season. Too high and you get scale on tiles, in the heater and inside the filter; too low (rare here, and usually in pools topped up with RO water) and the water becomes aggressive toward plaster and grout. Partial drain-and-refill is the only practical way down.

How to test properly

Test strips are convenient and roughly right for chlorine and pH, but unreliable for stabiliser and alkalinity. A liquid drop-test kit is far more accurate and inexpensive. Test at elbow depth away from returns, never immediately after dosing, and keep a simple log — the trend over weeks tells you far more than any single reading. Test chlorine and pH twice weekly in summer, alkalinity weekly, and stabiliser and calcium monthly.

Top Fixers pool maintenance contracts include full chemistry testing on every visit with readings recorded so you can see the trend, plus correction of all five parameters — not just a scoop of chlorine and a wave of the net.

Frequently Asked Questions

Why is my pool green even though I add chlorine?

Almost always because the chlorine cannot work: pH too high (above 7.8 chlorine loses most of its power), stabiliser too high causing chlorine lock, or stabiliser too low so UV destroys chlorine within hours. Test all three before adding more chlorine — more chlorine into a chemically broken pool is money down the drain.

How often should I test my pool water in the UAE?

Free chlorine and pH twice a week from May to September and weekly in cooler months; total alkalinity weekly; cyanuric acid and calcium hardness monthly. Heat, heavy use and dust storms all justify extra testing.

Is it safe to swim if the chemistry is off?

Low or zero free chlorine means the water is not sanitised — avoid swimming until it is corrected. Very high chlorine after shocking, or badly out-of-range pH, cause eye and skin irritation. When in doubt, test before swimming rather than after.