Red eyes and itchy skin after swimming are the most common complaints pool owners hear. Despite what everyone assumes, chlorine isn't usually the villain — combined chlorine (chloramines) and pH imbalance are. Once you know this, fixing it is fast.
The real cause: chloramines
When chlorine reacts with organic compounds — swimmer waste, body oils, urine, sweat — it forms chloramines (combined chlorine). Chloramines are the irritating compounds responsible for the strong "pool smell," red eyes, and skin irritation. A properly managed pool with low combined chlorine has almost no odor and causes minimal irritation.
Combined chlorine = Total chlorine − Free chlorine. Target CC below 0.2 ppm. Anything above 0.5 ppm causes noticeable irritation. Above 1.0 ppm is a significant problem.
pH and its role in irritation
Human eyes have a pH of approximately 7.4 — the same as well-balanced pool water. When pool pH drifts to 7.0 or below, the water becomes acidic enough to irritate mucous membranes directly. When pH climbs above 7.8, chlorine efficacy drops and organic buildup accelerates, indirectly causing more chloramine formation.
Diagnosing your situation
- Test free chlorine AND total chlorine (you need both readings to calculate combined chlorine)
- Test pH — target 7.4–7.6
- Check cyanuric acid (CYA) — if above 80 ppm, your actual available chlorine is far lower than the test reads, allowing organic buildup
The fix: breakpoint chlorination
To destroy chloramines you must reach breakpoint chlorination — raising FC to 10× the combined chlorine level. If CC is 1.0 ppm, you need to shock to 10 ppm FC and hold it there until the chloramines are fully oxidized (usually 4–8 hours with the pump running).
Use an unstabilized chlorine source for shocking — liquid chlorine or cal-hypo — not stabilized trichlor or dichlor tablets, which add more CYA.
Prevention
- Encourage pre-swim showers — this alone reduces chloramine formation by 50%+
- Weekly shock even when the pool "looks fine"
- Keep pH in 7.4–7.6 range consistently
- Monitor and manage CYA — partial drain and refill when CYA exceeds 80 ppm
If your pool “smells like chlorine,” it actually has too little effective chlorine and too many chloramines. Shock it — the smell will go away, not get worse.
Want a pro to handle this?
Our CPO-certified techs run this exact playbook on every weekly service visit.