Water, clarity and algae
Reading a pool water test result
A water test gives several numbers at once. Knowing which one to fix first saves chemicals and stops you chasing your own corrections.
A typical home or professional test shows free chlorine, total chlorine, pH and total alkalinity, and often calcium hardness, stabiliser and, in salt pools, salt. These values are linked: alkalinity governs how pH behaves, pH governs how well chlorine works, and stabiliser changes how much chlorine is needed to do the same job.
Water guides explain what a reading or a symptom means and the order in which to correct it.
The usual order is alkalinity first, then pH, then chlorine. Calcium hardness and stabiliser change slowly and are managed over weeks rather than at every visit. Dosing chlorine while pH is high, or adjusting pH while alkalinity is far out, usually means the correction has to be repeated within days.
The short version
Alkalinity first
It sets how stable pH will be after you adjust it.
Then pH
It decides how much of the chlorine is in its effective form.
Then chlorine
Dosed once balance is right, so the dose does its job.
What each number tells you
Free chlorine
The sanitiser available to kill bacteria and algae right now.
Combined chlorine
Total minus free: chlorine already tied up with contaminants, the source of smell and irritation.
Hardness and stabiliser
Slow-moving values that decide scale risk and chlorine efficiency, corrected gradually or by dilution.
For a test you can trust
Sample at elbow depth
Away from return jets, skimmers and any chemical feeder.
Test straight away
Chlorine and pH change once the sample is out of the pool.
Check reagent dates
Expired reagents and strips give misleading readings.
Common questions
Why do my readings differ from the technician’s?
Different methods, sample points and times of day give different results. Comparing like with like makes the trend clearer.
Do I need to test everything each time?
Free chlorine and pH most often; alkalinity weekly or so; hardness and stabiliser monthly.
What if every number is out?
Work through them in order — alkalinity, pH, chlorine — and retest between steps.
Related pool care guides
- Salt levels in a salt poolAnother water problem with a related cause.
- Phosphates in pool waterAnother water problem with a related cause.
- Stabilised or unstabilised chlorineA related choice about how the pool is looked after.
- Chlorine shock or non-chlorine shockA related choice about how the pool is looked after.
This guide sits under pool water treatment. Browse all pool care guides. We look after pools at homes and commercial properties across Dubai.
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Next step
Not sure what your test means?
Send us a photo of your results. We will explain what to adjust and in which order.