Pool Smells Like Chlorine? Why It Usually Means Too Little

A lot of people walk past a pool that smells strongly of chlorine and think it's been overdosed. Most of the time it's the opposite. That sharp, swimming-centre smell, along with red eyes and itchy skin after a swim, usually means the chlorine in the water is busy fighting waste and there isn't enough free chlorine left to finish the job. With more swimmers, more sunscreen and warmer water through a Brisbane summer, it's one of the most common things we see this time of year.

What you're actually smelling

When chlorine meets sweat, urine, body oils, sunscreen and other organic waste, it combines with it and forms compounds called chloramines, also known as combined chlorine. Chloramines are what give off the strong smell and irritate eyes and skin. They're also a much weaker sanitiser than free chlorine, so a pool can smell of chlorine and still be on its way to going cloudy or green.

Clean, properly chlorinated water has very little smell at all.

Free chlorine vs total chlorine

A test that only shows one chlorine number can't tell you this is happening. A test that reads both free chlorine and total chlorine can:

• Free chlorine is the chlorine still available to sanitise.
• Total chlorine is free chlorine plus the combined chlorine that's already been used up.
• The difference between the two is your combined chlorine. As a general guide, if total chlorine is more than about 0.5 ppm higher than free chlorine, chloramines are building up and the pool needs attention.

This is one reason we test the water properly every visit. Our article on why regular water testing is important covers the other readings that matter.

Common causes in summer

• Heavy use. A weekend of kids, visitors or a pool party puts a lot of waste into the water at once.
• Chlorine running too low. A chlorinator set for winter often can't keep up once the water warms and the pool gets used every day.
• Not enough stabiliser. Without it the sun burns chlorine off before it can do its work. See why pool chlorine disappears in summer.
• Poor circulation or a dirty filter. If the pump isn't running long enough or the filter is clogged, the water isn't being cleaned and treated evenly.
• Rain and runoff. Storm water washes leaves, dirt and garden debris into the pool and uses up chlorine fast.

How to clear it

The fix is to raise the free chlorine high enough to break down the chloramines. This is usually done with a shock treatment, either a non-chlorine oxidiser or a dose of chlorine sized to your pool.

• Test first so you know your free and total chlorine and your pH. Shock works best with pH in the normal range.
• Shock in the late afternoon or evening so the sun doesn't burn it straight off, with the pump running.
• Follow the product label for the dose for your pool size, and keep swimmers out until the chlorine is back in the normal range.
• Clean or backwash the filter and empty the baskets.
• Retest the next day. If the smell is gone and free and total chlorine are close together, you're back on track.

Then look at why it happened. If it keeps coming back, the chlorinator output, the pump running time or the stabiliser level usually needs adjusting for summer.

Keeping it from coming back

• Shower before swimming. It makes a real difference to how much waste goes into the water.
• Lift the chlorinator output or running hours as the weather warms, and check the cell is clean. Our guide on how to check and clean your cell shows you how.
• Test more often after heavy use or storms.
• Keep the filter clean so the water is being treated properly.

If your pool smells strongly of chlorine or the water is stinging eyes, bring a water sample into our shop at 304-306 Junction Rd, Clayfield and we'll test it for you, or call (07) 3857 8530. If you'd rather not deal with it yourself, book a service and one of our technicians will test, balance and treat the water and check the equipment while they're there.