Pool with Strong Chlorine Smell: How to Fix

Introduction

Have you ever entered a pool with such a strong chlorine smell that it irritated your eyes and nose? Interestingly, this intense smell doesn't mean the pool has too much chlorine – in fact, it indicates exactly the opposite. What you're smelling isn't free chlorine, but rather chloramines, a by-product that forms when there are contaminants in the water and insufficient chlorine to neutralise them.

This is one of the most persistent myths about pools: many people think the "pool smell" is normal and a sign of well-treated water, when in reality it indicates a water quality problem that needs to be corrected.

In Margem Sul, especially in condominium, hotel, and public pools with heavy use, this problem is common during summer. In this article, we'll explain the science behind the chlorine smell, how to correct it, and how to keep your pool free of unpleasant odours.

The Truth About the Chlorine Smell

What Are Chloramines?

When you add chlorine to the pool, it reacts with organic contaminants present in the water:

• Sweat and body oils
• Urine (yes, it's common)
• Sunscreens and cosmetics
• Dead skin cells
• Saliva

This chemical reaction forms compounds called chloramines, mainly:

• Monochloramine (NH₂Cl)
• Dichloramine (NHCl₂)
• Trichloramine (NCl₃) – the most irritating

Trichloramine is particularly volatile and is responsible for the characteristic "pool smell." It's also the main cause of eye, nose, and respiratory irritation.

Free Chlorine vs Combined Chlorine

To understand the problem, it's important to distinguish:

The ideal is to have high free chlorine and very low combined chlorine (less than 0.5 ppm).

Why Your Pool Smells Like Chlorine

Main Causes

1. Insufficient free chlorine: Not enough chlorine to "burn off" contaminants
2. High pH: Above 7.6, chlorine loses effectiveness
3. Intensive use: Many swimmers introduce more contaminants
4. No pre-shower: Swimmers enter without washing
5. Insufficient ventilation: In indoor pools, chloramines accumulate
6. Excessive stabiliser: Blocks chlorine action

Aggravating Factors in Margem Sul

• Hot, long summers: More use, more contaminants
• Condominium pools: Many users, difficult to control hygiene
• Parties and events: Concentrated usage peaks
• Covered or semi-covered pools: Less natural ventilation

How to Eliminate the Chlorine Smell

Step 1: Test the Water Correctly

Use a kit that tests free chlorine AND total chlorine:

Combined chlorine calculation: Combined chlorine = Total chlorine - Free chlorine

If combined chlorine is greater than 0.5 ppm, it's time to act.

Step 2: Adjust pH

Before any treatment:

• pH should be between 7.2-7.4
• At pH 7.2, ~65% of chlorine is active
• At pH 8.0, only ~22% is active

Adjusting pH first maximises the effectiveness of the following treatment.

Step 3: Shock Treatment (Breakpoint Chlorination)

The goal is to raise free chlorine to a level that "breaks" the chloramines:

Rule of thumb: Shock dose = Combined chlorine × 10

Example: If combined chlorine is 1.5 ppm, you need to raise free chlorine to 15 ppm.

Procedure:

1. Perform treatment at end of day or at night
2. Use non-stabilised shock chlorine (calcium hypochlorite)
3. Distribute evenly throughout the pool
4. Keep pump running 8-12 hours
5. No swimming until chlorine drops below 3 ppm

Step 4: Ventilation (Indoor Pools)

If the pool is covered or indoor:

• Increase ventilation during and after shock
• Open windows or doors if possible
• Chloramines are volatile and disperse with fresh air
• In commercial pools, check the HVAC system

Step 5: Ongoing Maintenance

After solving the immediate problem:

• Test free and combined chlorine 2-3 times per week
• Do weekly preventive shocks (smaller dose)
• Maintain pH consistently between 7.2-7.6

Preventing the Chlorine Smell

Hygiene Rules

Implement these rules to reduce contaminant load:

• Mandatory shower before entering the pool
• No urinating in the pool (seems obvious, but...)
• Remove cosmetics before swimming
• Wear swim cap to contain hair
• Wash feet in the walkway area

Preventive Maintenance

• Weekly shock: Especially during peak usage season
• Regular monitoring: Test water frequently
• Adequate filtration: Pump running sufficient time
• Cover: Using when not in use reduces contamination

For High-Use Pools

In condominium, hotel, or public pools:

• Consider automatic dosing systems
• Install showers at the pool entrance
• Post hygiene notices
• Increase shock frequency in summer

Alternative Treatment Systems

If the chloramine problem is recurring, consider complementary systems:

UV Systems

• Ultraviolet light destroys chloramines
• Reduces need for chemical shock
• High initial investment but low maintenance

Ozone

• Powerful oxidiser that eliminates chloramines
• Significantly reduces chlorine needed
• More common in commercial pools

Salt Electrolysis

• Produces chlorine continuously from salt
• More stable chlorine levels
• Fewer chloramine peaks
• Popular in residential pools in Margem Sul

Copper/Silver Ionisation

• Complements chlorine with metal ions
• Allows less chlorine use
• Reduces chloramine formation

Dangers of Chloramines

Chloramines aren't just unpleasant – they can affect health:

Common Symptoms

• Eye irritation (redness, burning)
• Nasal and throat irritation
• Coughing, especially after swimming
• Dry, irritated skin
• Dry, brittle hair

Risk Groups

• Asthmatics: Can trigger attacks
• Frequent swimmers: Cumulative exposure
• Children: More sensitive
• Pool workers: Prolonged exposure

In Indoor Pools

Risk is higher because chloramines accumulate:

• Trichloramine concentrates at water level
• Swimmers breathe contaminated air
• Inadequate ventilation worsens the problem

Special Cases

Condominium Pools

In Margem Sul, many condominiums have shared pools:

• Difficult to control who showers
• High use in summer
• Management sometimes neglected

Recommendations:

• Post clear visible rules
• Install mandatory showers at entrance
• Hire regular professional maintenance
• Do more frequent water analyses

Small/Private Pools

In family pools:

• Small volume = less dilution
• Fewer users but same concentration
• Easier to implement control

Recommendations:

• Insist on shower before swimming
• More frequent shocks in summer
• Don't "save" on chlorine

Costs and Products

For Shock Treatment

For Regular Prevention

Frequently Asked Questions

If the pool smells like chlorine, should I add less chlorine?

No, it's the opposite. The smell indicates chloramines, which form when there's insufficient chlorine. The solution is to shock to destroy the chloramines.

Is it safe to swim in a pool with strong chlorine smell?

It's not ideal. The smell indicates the presence of chloramines that can irritate eyes, skin, and airways. It's better to solve the problem before swimming.

How long after shock can I swim?

Wait until free chlorine drops below 3 ppm, ideally between 1-3 ppm. Usually takes 24-48 hours.

Why do public pools smell more like chlorine?

More users = more contaminants = more chloramines. Additionally, not everyone showers before entering, and hygiene control is more difficult.

Does salt eliminate the chloramine problem?

Saltwater pools still use chlorine (produced by electrolysis), so they can still form chloramines. However, because chlorine is produced continuously, levels are more stable and the problem is generally less severe.

Conclusion

Strong chlorine smell in the pool is not a sign of excess chlorine – it's exactly the opposite. It indicates the presence of chloramines, formed when chlorine reacts with organic contaminants. Key points for solving and preventing this problem are:

• Understand that strong smell = lack of free chlorine
• Test free AND combined chlorine regularly
• Do shock treatment when chloramines are high
• Maintain pH between 7.2-7.6 for maximum chlorine effectiveness
• Implement good hygiene practices to reduce contaminants

If you need professional help with your pool in Margem Sul, ManutençãoPiscinas is here to help. Contact us for a no-obligation quote.