Introduction
There is one confusion that causes more health problems in pools than any other: people associate a strong chlorine smell and red eyes with too much disinfectant. In most cases, it is the opposite.
The strong smell does not come from free chlorine: it comes from chloramines — compounds formed when the disinfectant reacts with sweat, urine, creams and organic matter. They are what irritate eyes and airways. A pool that smells strongly does not have too much chlorine: it has too much contamination and, very often, too little available disinfectant.
This article explains which parameters affect health, by what mechanism, and what to do with each reading.
The Parameters That Affect Health
| Parameter | Why it matters for health | Effect when out of range |
|---|---|---|
| Free disinfectant | Kills pathogens | Insufficient: infection risk |
| pH | Determines disinfectant effectiveness and eye comfort | Out of range: irritation and ineffective disinfection |
| Chloramines (combined chlorine) | Irritant compounds | Strong smell, red eyes, coughing |
| Turbidity | Indicator of filtration and of risk | Cloudy water hides the bottom — a direct risk |
| Total alkalinity | Stabilises pH | Unstable pH, constant corrections |
| Calcium hardness | Comfort and scale | Deposits, cloudy water |
| Stabiliser (cyanuric acid) | Protects chlorine from UV | In excess, blocks chlorine's action |
The first two are what decide the sanitary safety of the water. In practice, all the others exist so that those two can stay where they should be.
Why pH Is the Most Important Parameter Nobody Measures
Two reasons, both health-related:
1. Eye comfort. Human tear fluid has a pH close to neutral. Water significantly away from that value irritates the ocular surface directly — with chlorine having nothing to do with it. Much "chlorine irritation" is pH irritation.
2. Disinfectant effectiveness. This is the decisive part. Chlorine in water exists in two forms, and the proportion between them depends on pH. With high pH, most of the chlorine is in the less effective form — meaning the chlorine reading on your kit can be correct while disinfection is working badly.
Practical consequence: uncontrolled pH produces irritation and infection risk at the same time, with a chlorine figure that looks fine on paper. It is the most misleading situation in pool maintenance.
See How to Balance Pool pH and Pool Water Irritating Your Eyes.
Chloramines: the Smell That Gets Misread
How they form: the disinfectant reacts with nitrogen of organic origin — sweat, urine, saliva, cream residues, skin cells — and forms combined compounds.
What they cause: an intense characteristic smell, eye irritation, airway irritation, coughing.
What they tell you: that there is accumulated organic load and that the disinfectant is being consumed combining rather than disinfecting.
What you do: not reduce the chlorine — increase oxidising capacity to destroy the combined compounds, through a shock treatment, while reducing the incoming organic load.
How you prevent them: shower before getting in, do not urinate in the water, remove excess creams and oils, and filter enough.
See Pool with a Strong Chlorine Smell.
💡 Dica Profissional
Measure **total chlorine** and **free chlorine**, not just one of them. The difference between the two is combined chlorine — the chloramines. If that difference is significant, you have the explanation for the smell and the irritation, and you know the problem is organic load, not excess disinfectant. It is the most useful measurement and the least performed in domestic pools.
Turbidity: More Than Cosmetic
Cloudy water is a health problem in two ways:
A direct safety risk: if you cannot see the bottom, you cannot see a submerged person. It is why, in collective-use pools, cloudy water is grounds for immediate closure.
An indicator of treatment failure: turbidity means particles are not being removed, and what stays in suspension includes organic matter that consumes disinfectant and can harbour microorganisms.
Most frequent causes: insufficient filtration, sand at end of life, uncontrolled pH and hardness, a bather load beyond the treatment capacity. See Clogged Sand Filter and When to Replace Filter Sand.
The Stabiliser Nobody Watches
Cyanuric acid protects chlorine from UV degradation, which is why it is present in many stabilised chlorine products. The problem is that it is not consumed: it accumulates with every dose, over the seasons.
When it builds up too far, the chlorine becomes "locked" — present in the reading, with little effective disinfecting capacity. The result is the classic situation: the kit shows enough chlorine, the water is cloudy or has algae, and additional doses solve nothing.
How it is detected: by measuring. It is not a parameter you can see.
How it is solved: only by dilution — partial water replacement. There is no product that reduces it.
How it is avoided: alternating between stabilised and unstabilised products, rather than always using the same one.
Who Is Most Exposed
- Children. They swallow more water, spend more time in it and are closer to the surface, where the concentration of irritant compounds is highest. See Safe Pool for Children: Equipment.
- People with asthma or respiratory hypersensitivity. Volatile chloramines are the determining factor, especially in indoor spaces with insufficient ventilation.
- People with sensitive skin or dermatitis. Out-of-range pH aggravates it directly.
- Immunocompromised people. A smaller margin against disinfection failures.
See Pool for People with Allergies.
The Routine That Protects
Two to three times a week in the use season:
- pH and free disinfectant
Once a week:
- Total chlorine, to calculate the combined figure
- Total alkalinity
Once a month:
- Calcium hardness
- Stabiliser
Always:
- Write it down. A single reading tells you nothing; a series shows trends and lets you anticipate problems instead of reacting to them.
A water-analysis log template solves the format. See also How to Use a Water Test Kit.
When Not to Get In
- Cloudy or coloured water
- A strong, persistent smell
- Disinfectant absent or very low on the reading
- After a shock treatment, until the values are back within the normal range
- With a gastrointestinal illness in progress — out of consideration for other users
- With open wounds
Common Mistakes
Reading a strong smell as excess chlorine. It is almost always the opposite: chloramines from organic load and insufficient free disinfectant.
Measuring only chlorine. Without pH, the chlorine figure does not tell you whether disinfection is working.
Never measuring the stabiliser. It is the parameter that explains the "enough chlorine and bad water" cases.
Reducing the disinfectant because someone has red eyes. Red eyes are usually pH or chloramines. Reducing the chlorine makes both worse.
Dosing without measuring. It produces swings that make bathers uncomfortable and waste product.
Not showering before getting in. It is the individual measure that most reduces chloramine formation.
Under-filtering. No product compensates for insufficient filtration.
Frequently Asked Questions
Does a strong chlorine smell mean too much chlorine?
Almost always the opposite. The smell comes from chloramines, formed when the disinfectant reacts with organic matter. It indicates a high organic load and frequently insufficient free disinfectant.
Why do my eyes go red in the pool?
In most cases, because the pH is away from the appropriate range, or because of chloramines. Free chlorine at a correct level does not cause significant eye irritation.
What values should I maintain?
Follow the indications from the manufacturer of your products and your test kit, and keep the values stable within the range given. What matters is measuring regularly and recording it — stability matters more than chasing an exact number.
What do I do if the kit shows chlorine but the water is bad?
Measure the stabiliser and the pH. The two most frequent explanations are accumulated stabiliser, which blocks chlorine's action, and high pH, which reduces its effectiveness.
Is a saltwater pool healthier?
It is more comfortable for many people, because there is less product handling and the concentration is more stable. But it disinfects on the same principle: it generates chlorine from salt. pH remains the critical parameter. See Saltwater Pool Maintenance.
How long after a shock treatment can you get in?
Until the values are back within the normal range, confirmed by measurement — not by elapsed time. Measure before letting anyone in.
Conclusion
A pool's water quality is not judged by looks or by smell. It is judged with a test kit, and the parameter that most determines health and comfort is the one fewest people measure: pH.
Key points to remember:
- A strong chlorine smell signals chloramines and organic load, not excess disinfectant.
- With high pH, the measured chlorine can be correct while disinfection is failing.
- Measure free chlorine and total chlorine: the difference is the chloramines.
- Accumulated stabiliser locks up chlorine and is only resolved by dilution.
- Cloudy water is a safety risk, not just a cosmetic matter.
- Showering before getting in is the most effective individual measure.
If you want to know the real state of your pool water, the on-site technical diagnosis measures pH, free and total disinfectant, alkalinity, hardness and stabiliser, and gives you the values and the corrections in writing. It costs €45, deductible from your first month under contract.
