When it comes to pool and spa water quality, chlorine is both essential and challenging. It’s the cornerstone of sanitation — protecting bathers from harmful bacteria, viruses and protozoa — yet it can also produce irritating by-products when not properly managed.
Understanding how to balance the good, the bad and the harmful sides of chlorine is key to safeguarding public health, maintaining compliance and delivering a safe, comfortable environment for swimmers and staff alike.
The Good: Free Chlorine
Free chlorine is the active disinfectant in your pool or spa water. In the right concentration and pH range (7.2–7.8) it forms hypochlorous acid (HOCl) — a powerful oxidiser that kills bacteria and viruses within seconds.
Maintaining correct free chlorine levels ensures:
• Rapid pathogen kill times (e.g. E. coli in <1 minute)
• Crystal-clear water and reduced biofilm risk
• Compliance with state health department guidelines
• A safe, hygienic environment for all bathers
However the effectiveness of free chlorine depends heavily on pH control and ORP (Oxidation-Reduction Potential). As pH rises chlorine becomes less reactive; at pH 8.0 only around 24% remains active. Regular testing and calibration of your controller are essential to maintain effective disinfection.
The Bad: Combined Chlorine
Combined chlorine — often referred to as chloramines — forms when free chlorine reacts with organic matter such as sweat, body oils, urine, cosmetics and other waste introduced by bathers.
While this is a normal part of the disinfection process high levels of combined chlorine are a warning sign that your pool is struggling to oxidise contaminants fast enough.
Excessive combined chlorine causes:
• Eye, skin and respiratory irritation
• The strong “chlorine smell” often mistaken for cleanliness
• Cloudy water and unpleasant air quality
• Decreased disinfection efficiency
• Health department non-compliance (combined chlorine ideally < 0.5 ppm, health guidelines < 1 ppm)
If left unchecked, it can quickly affect both bather comfort and operational performance.
The Harmful: Chloramine Gas and Facility Damage
Chloramines don’t just stay in the water — they release into the air above the pool. In enclosed environments, this can become a serious issue for both people and infrastructure.
Over time, chloramine gases can:
• Corrode metal structures, ceiling fittings and electronic components
• Accelerate wear of filters, pumps and HVAC systems
• Create odour, haze and discomfort for staff and users
• Increase maintenance costs and trigger costly shutdowns
In short, uncontrolled combined chlorine becomes a hidden operational hazard — impacting everything from compliance to customer satisfaction.
The Solution: Secondary Disinfection and Oxidation Support
Chlorine alone can’t do all the work. To maintain truly healthy, clear and compliant water, modern pool operations increasingly rely on secondary sanitation systems that support chlorine’s role.
Ultraviolet (UV) Light
UV light inactivates microorganisms by damaging their DNA. It’s particularly effective against chlorine-resistant pathogens such as Cryptosporidium and Giardia and it helps reduce chloramine formation by breaking down some organic compounds before they react with chlorine.
Advanced Oxidation Process (AOP)
AOP systems combine UV and ozone generation to create hydroxyl radicals (•OH) — the most powerful oxidisers available for water treatment. Within the AOP chamber, the UV light immediately destroys any residual ozone before the water returns to the pool, ensuring no ozone exposure or off-gassing occurs.
Advanced oxidation uses the same scientific principles outlined in HealthySwim’s research on secondary sanitation technology — hydroxyl radicals react rapidly with complex organic compounds, converting them into harmless end products such as CO₂ and H₂O. Secondary sanitation is recommended by health departments across Australia as the most effective treatment for resistant pathogens and organic matter.
These hydroxyl radicals destroy chloramines on contact, neutralising odour and irritation while improving overall air and water quality. This technology is recognised in the industry as one of the most effective defences against combined chlorine build-up and disinfection by-products.
To learn more about how secondary sanitation technologies deactivate viruses, see our related article: “Viruses Deactivated and Destroyed by Secondary Sanitation Technology” (https://healthyswim.com.au/viruses-deactivated-and-destroyed-by-secondary-sanitation-technology/).
For more on how AOP works, read our detailed science summary: HealthySwim AOP Technology Explained 👉 here
The Pay-Off: Healthier, Happier Pools
By managing combined chlorine effectively — through balanced chemistry, testing and appropriate secondary disinfection — operators can achieve:
• Improved bather comfort and satisfaction
• Enhanced indoor air quality for staff and users
• Reduced corrosion and lower maintenance costs
• Regulatory compliance and audit readiness
• Sustainable operation with less water and chemical waste
Good water management isn’t just about meeting standards — it’s about protecting people, property and your reputation.
HealthySwim – Protecting Health, Compliance and Comfort
HealthySwim supports resorts, aquatic, spa and recreation facilities across Australia and New Zealand with compliance training, water testing and technical expertise.
Together, we can help ensure that the good side of chlorine always wins.
