Why Does My Pool Smell Strongly of Chlorine?

The heavy chlorine smell around a pool is not chlorine. It is chloramines, the compounds formed when free chlorine combines with sweat, body oils, urine, sunscreen, lotions and other organic material. Properly sanitized water has almost no smell at all.

Which means the smell is backwards from what most people assume. It signals too little effective chlorine, not too much. The fix is more chlorine, not less.

What chloramines are and why they stink

Free chlorine attacks contaminants. When it binds to nitrogen compounds it becomes combined chlorine, and combined chlorine is what your nose picks up. It is also a weak sanitizer, roughly a small fraction as effective as free chlorine, and it is what causes:

• Burning, red eyes
• Itchy or irritated skin
• That sharp indoor-pool odor
• Dull or slightly cloudy water

If your eyes sting in a pool, people usually blame “too much chlorine.” It is nearly always chloramines and off-target pH instead.

Measure it before you treat it

You need a test that reads both free chlorine and total chlorine. The difference between them is your combined chlorine.

Combined chlorine = total chlorine minus free chlorine

• Below 0.2 ppm is fine
• 0.2 to 0.5 ppm is worth watching
• Above 0.5 ppm means shock the pool

Standard test strips generally will not give you this. A DPD drop kit or a good digital tester will.

How to clear it out

Chloramines are destroyed by breakpoint chlorination, which means raising free chlorine high enough to blow the molecules apart. The accepted target is roughly 10 times your combined chlorine reading.

If combined chlorine is 0.6 ppm, you need to reach about 6 ppm free chlorine above your current level.

Practical dosing: about 1 gallon of 12.5 percent liquid chlorine per 10,000 gallons raises free chlorine roughly 10 ppm.

Do it this way:

1. Test free and total chlorine, and check pH
2. Bring pH to 7.2 to 7.4 first, since chlorine works better at the low end of range
3. Add the shock at dusk or after dark so sunlight does not destroy it
4. Run the pump overnight, at least 8 hours
5. Retest in the morning and keep swimmers out until free chlorine is back under 4 ppm

Half-shocking is worse than not shocking. If you stop short of breakpoint you create more chloramines than you destroy, and the smell gets stronger.

Why it keeps coming back

If the odor returns within days, look at the underlying cause:

• Heavy bather load without enough chlorine to keep up
• Cyanuric acid above 100 ppm slowing your chlorine down
• Poor circulation or too few pump run hours
• A dirty filter
• Guests not rinsing before swimming (sunscreen and lotion are major contributors)
• Chronically high pH keeping chlorine ineffective

The Keys angle

Sunscreen is a year-round load here in a way it is not in seasonal climates. Between the sun, the salt air and the fact that people are in and out of the water twelve months a year, Key West pools take a constant organic input that never gets a winter pause to catch up.

Vacation rental pools are the ones we see with the worst chloramine problems. A property that fills and empties every few days sees big, irregular bather loads, and a pool that was clean on Tuesday can smell sharp by Saturday afternoon. Storm season adds blown-in organic debris on top of it.

If your pool smells like a public locker room, test for combined chlorine and shock it properly, because the odor is your water telling you the sanitizer is losing.