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Chlorine is a potent and reliable disinfectant that kills bacteria, algae, viruses, and other pathogens, helping to protect public health and maintain safe swimming environments. In most public swimming pools the chlorine level is controlled automatically using a pool controller.

When chlorine dissolves in water, it forms hypochlorous acid (HOCl) and hypochlorite ions, which act by destroying microorganisms’ cell structures and metabolic systems.

• UK (PWTAG guidelines): With pH at 7.0–7.2, free chlorine should be 0.75–1 mg/L; if pH is 7.2–7.4, free chlorine should be around 2 mg/L. Free chlorine should not exceed 3 mg/L, and if levels reach 5 mg/L, treatment must stop until corrected.

  · US (CDC / MAHC): Minimum free chlorine of 1 ppm; if using cyanuric acid, minimum is 2 ppm; maximum safe level generally around 10 ppm. pH should be 7.2–7.8.

· Manual testing: Before opening, every two hours during operation, and after closing.

· Automatic systems: Still require manual spot checks at least three times daily; controllers should be calibrated daily.

· CDC guidance (US): Test disinfectant and pH at least twice a day and hourly during heavy use.

These guidelines are irrespective of whether or not the swimming pool pH and free chlorine are controlled by a pool controller.

• Yes—as long as levels stay within recommended limits, chlorine is safe. However, chloramines (combined chlorine) formed when chlorine reacts with contaminants can irritate eyes, skin, and airways.

• Yes. Inadequate chlorine can allow pathogens (like bacteria or parasites) to survive, raising the risk of illnesses such as diarrhoea or skin infections. Poor chlorine control can be eliminated by the use of a pool controller.

Overexposure—especially to chloramines—may cause:

· Skin rashes or dryness
· Burning or red eyes
· Respiratory irritation (common indoors)
· Strong “chlorine smell” often signals excessive chloramines, not cleanliness

While specific virus data wasn’t in these sources, chlorine (in the form of hypochlorous acid) is known to inactivate a broad range of pathogens, including many viruses, as part of general disinfection.

This irritation is usually caused by chloramines, which form when chlorine reacts with sweat, urine, or other organic matter; these compounds are less effective at disinfecting and known for irritating mucous membranes.

Yes, as long as water chemistry is well-balanced and chlorine levels are controlled. Their delicate skin and eyes require especially good water balance and hygiene—operators should stress pre-swim showers and diaper checks.

Chlorine is typically introduced via:

· Liquid hypochlorite
· Chlorine tablets (e.g. trichlor)
· Automated dosing using a pool controller.

· Free chlorine: Active chlorine available for disinfection.

· Combined chlorine (chloramines): Formed when free chlorine bonds with contaminants; less effective and irritating.

· Total chlorine = Free + Combined. Combined chlorine should be kept below 0.4 ppm (or under half of free chlorine), and if exceeded, the pool water usually needs shocking.

· Too low: Risk of pathogens surviving and spreading illnesses.

· Too high: Causes swimmer irritation; guidelines indicate that if free chlorine exceeds 3 mg/L (UK) or recommended upper limit of 10ppm (US), dosing must be stopped until levels fall to a safe range.

Common supplementary adjustments include:

· pH control agents (e.g. acids, sodium bicarbonate)

· Secondary disinfection (UV or ozone) to reduce chloramines and chlorine demand

· Balancing additives: calcium hardness, alkalinity, cyanuric acid (with limits).

If chlorine levels spike (e.g., above 5 mg/L UK), dosing must be halted immediately; if levels continue rising or are unsafe, pool use must cease until restored to safe range. These conditions can largely be eliminated by the use of an automatic chemical dosing pool controller.

Requirements vary by country:

· UK (PWTAG): Free chlorine target 0.75–2 mg/L, max 3 mg/L; combined chlorine <1 mg/L (or <50 % of free).

· US (CDC/MAHC): Minimum free chlorine 1–2 ppm depending on cyanuric acid usage; maximum around 10 ppm. Always check local health codes.

· US: CDC provides the Model Aquatic Health Code (MAHC), alongside local and state health departments.

· UK: Guidance primarily from PWTAG, though enforcement is via local authorities.

Inspectors typically review manual logbooks and verify automatic sensor outputs; they may test water directly, check calibration protocols, and ensure testing frequency meets standards.

Look for posted test records, observe water clarity, note the absence of strong “chlorine smell” (which often indicates chloramines, not cleanliness), and pay attention to any eye or skin discomfort, which may signal a chemical imbalance.

Operators should be trained in water chemistry, safe chemical handling, automatic control systems, emergency protocols, legal compliance, and how to respond to contamination incidents. CDC and MAHC offer training frameworks for certification.