Aquarius: Are your pool readings lying? The hidden chlorine threat every school needs to know
Combined chlorine (chloramines) poses a major challenge for swimming pool operators.
Beyond being a recognised health concern, they can also disrupt the performance of membrane-based sensors that measure free chlorine.
Effects of combined chlorine
Chloramines can interfere with readings by causing false highs or slowing sensor response due to cross-sensitivity, and their slower diffusion through membranes compared to HOCl further reduces responsiveness and recovery time. They can also foul membranes as reaction byproducts accumulate on the surface, decreasing permeability. Because chloramines become more disruptive at higher pH levels, they can distort measurements and contribute to calibration issues, leading sensors calibrated for free chlorine to overestimate chlorine levels when chloramines are present.
How combined chlorine harms membranes
High combined chlorine levels damage membranes by causing oxidative stress that breaks down polymer chains, forming sticky byproducts that foul the surface, and creating pH and ammonia interactions that weaken adhesives and materials. The membrane can swell as it absorbs chloramine-rich water, leading to altered diffusion and long-term brittleness.
Isopropyl alcohol and membrane sensors
Isopropyl alcohol can be used for light, occasional surface cleaning of membrane sensors, provided it is applied sparingly and thoroughly rinsed afterward. However, it cannot reverse or repair chemical damage to the membrane, and prolonged exposure may cause swelling or brittleness.
In general, IPA does not penetrate intact hydrophobic membranes, but if the membrane is cracked, worn, or chemically degraded, it can seep through and contaminate the sensor.
Reducing combined chlorine in swimming pools
Step one: Test levels
Measure free and combined chlorine and record results.
Step two: Apply breakpoint chlorination
Dose chlorine at ten times the combined chlorine level (e.g., if the reading is 0.5 ppm, raise to 5 ppm) and distribute evenly.
Step three: Use non-chlorine shock
Potassium monopersulfate reduces chloramines without raising chlorine.
Step four: Improve circulation and filtration
Ensure pumps and filters work efficiently and clean filters regularly to remove contaminants.
Step five: Maintain water chemistry
Keep free chlorine within state or regional guidelines and pH between 7.2–7.6.
Step six: Reduce contaminants
Encourage pre-swim showers to limit sweat and product residues.
Step seven: Add UV or ozone
Install UV or ozone systems for continuous chloramine control.
Partner with Aquarius Technologies to understand and elevate your pool water quality
Advanced Oxidation Process (AOP) combines UV light and oxidising agents (usually ozone or hydrogen peroxide) to create hydroxyl radicals (•OH). Hydroxyl radicals are extremely reactive and can destroy organic matter, chloramines, and pathogens quickly.
By partnering with Aquarius Technologies, school and university pool operators can maintain accurate chlorine readings, protect sensor integrity, and ensure a safer, more comfortable swimming environment. Regular monitoring, proper chemical management, and the integration of advanced technologies such as UV, ozone, or AOP systems will minimise chloramine buildup and improve overall water quality.
Contact Aquarius Technologies to implement these strategies today and safeguard swimmers, optimise sensor performance, and maintain crystal-clear, healthy pool water for your students.
07 3274 4750
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aquariustech.com.au
