Domakihub How to Reduce Combined Chlorine in Your Pool
Chloramines cause red eyes and that sharp smell — here is how to measure and eliminate them for good.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
That familiar pungent pool smell and stinging eyes are not signs of too much chlorine — they are signs of combined chlorine, also called chloramines, which form when free chlorine reacts with sweat, sunscreen, and urine. The video above demonstrates exactly how to test a water sample and confirm whether combined chlorine is your problem, while this guide walks you through the corrective steps in practical order. Whether you manage a private villa, a holiday rental, or a hotel pool in Greece, controlling chloramines is one of the fastest ways to improve swimmer comfort and protect your equipment.
What Is Combined Chlorine and Why Does It Matter?
Free chlorine is the active sanitiser dissolved in your pool water. When it reacts with nitrogen-containing compounds from swimmers — sweat, body oils, and ammonia from urine — it binds with those compounds to form chloramines, which chemists call combined chlorine. Chloramines are far less effective at killing bacteria than free chlorine, so a pool high in chloramines can feel aggressively chemical yet still carry a microbial risk.
The industry measure is simple: total chlorine minus free chlorine equals combined chlorine. Most guidelines recommend keeping combined chlorine below 0.2 ppm. Values above that threshold are responsible for the eye irritation, skin dryness, and strong odour that swimmers often wrongly blame on excessive chlorine.
How Often Does This Become a Problem in Greece?
Greek conditions accelerate chloramine build-up in two ways. Intense summer UV degrades free chlorine very quickly, which means pool owners often dose more aggressively to compensate, creating a larger reservoir of compounds that can bind and form chloramines. Heavy bather loads on holiday rental or hotel pools compound the issue because each swimmer introduces nitrogen into the water.
Pools that are partially shaded or covered overnight tend to retain more chloramines because UV light and evaporation — two natural pathways for off-gassing chloramines — are reduced. Regular testing is the only reliable way to catch the problem before it becomes visible or odorous.
How to Test and Treat Combined Chlorine Step by Step
- 1
Test your free and total chlorine levels
Use a DPD test kit rather than simple test strips — the DPD method measures both free chlorine (DPD No. 1 reagent) and total chlorine (DPD No. 3 reagent) separately. Subtract free from total to get your combined chlorine figure. A reliable reading requires a fresh sample taken mid-pool at elbow depth, away from return jets, as shown in the video above.
- 2
Calculate your breakpoint chlorination dose
To destroy chloramines you must dose free chlorine to a concentration roughly ten times your combined chlorine reading — this is called breakpoint chlorination. For example, if combined chlorine sits at 0.5 ppm, you need to raise free chlorine by at least 5 ppm above its current level. Calculate the volume of your pool in cubic metres and use the product label to convert that target rise into the correct weight or volume of shock product.
- 3
Choose between chlorine shock and non-chlorine shock
Granular calcium hypochlorite (65-70% available chlorine) or liquid sodium hypochlorite are the traditional options for breakpoint chlorination; they drive free chlorine to the breakpoint and oxidise chloramines directly. Potassium monopersulfate (non-chlorine shock) is an alternative that oxidises organic waste without adding to chlorine chemistry — useful when a pool must reopen within an hour, but note it does not raise free chlorine, so it is most effective when combined chlorine levels are moderate rather than severe.
- 4
Shock at dusk and keep the pump running overnight
Dose the shock product in the evening to prevent UV from burning off the elevated free chlorine before it has time to work. Pre-dissolve granular products in a bucket of water before pouring slowly around the pool perimeter with the pump running. Run filtration continuously for at least eight hours. If combined chlorine was very high, re-test in the morning; a second shock dose is sometimes needed before levels drop below 0.2 ppm.
- 5
Prevent re-accumulation with routine practices
Once chloramine levels are correct, keep them there by maintaining free chlorine between 1 and 3 ppm at all times, testing twice weekly during peak season. Encourage swimmers to shower before entering — this is especially important in rental and hotel settings and required by Greek health authority guidelines for commercial pools. Backwash or rinse your filter after the treatment cycle, since chloramines partially bind to filter media and can be re-released into the water if the filter is neglected.
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FAQ
- Can I swim in the pool immediately after shocking for chloramines?
- Not straight away. After a chlorine shock, wait until free chlorine has dropped back to 3 ppm or below before allowing swimmers in — this typically takes several hours in warm, sunny Greek weather. If you used a non-chlorine shock product and your free chlorine was already in range, most manufacturers allow re-entry after 15 to 30 minutes, but always verify with your specific product label.
- Why does my pool still smell strongly even though the free chlorine test reads fine?
- A normal or even high free chlorine reading does not rule out a chloramine problem. The characteristic sharp, medicinal smell comes from chloramines, not from free chlorine itself. Test total chlorine alongside free chlorine and calculate the difference — if combined chlorine is above 0.2 ppm, that is your source of odour, and shock treatment is the correct response, not reducing your chlorine dose.
- How often should holiday rental and hotel pools in Greece test for combined chlorine?
- Commercial and high-bather pools should test free and total chlorine at least twice daily during the peak season (May through September). Combined chlorine should be specifically checked at least twice a week, and immediately after any particularly heavy use period such as a full villa rental changeover weekend. Greek EODY guidelines for public pools also require a logbook of chemical readings, so systematic testing serves both water quality and compliance.