Why does your pool smell “fishy” or like chlorine – and how to fix It
If you’ve ever wondered, “Should my pool really smell so strongly of chlorine?” — the answer is no. A well-maintained pool should have almost no smell.
A strong chemical odor is not a sign that your pool is clean. On the contrary, it usually means something in the water is off. The good news? You can fix it.
Why does your pool smell?
The smell doesn’t come from chlorine itself. It comes from chloramines — chemicals that form when chlorine reacts with any nitrogen compounds. Sweat, urine, skin, hairs… all these are nitrogen compounds which contribute to chloramines increase. • Monochloramine: mild, builds up over time. • Dichloramine & Trichloramine: strong-smelling, irritating, and less effective at keeping water clean.
In short: the smell means your pool chemistry is out of balance. It’s not that there’s too much chlorine, it’s that the chlorine is fighting to neutralise contaminants that are being introduced into the water generally by the users.
Indirect Effect of Sulphates
Although sulphates themselves do not form chloramines, high levels can indirectly affect water quality: • Increased TDS: high sulphates raise total dissolved solids (TDS), which can slightly reduce chlorine efficiency, increase conductivity, and affect ORP readings. Usually, this is minor unless sulphates exceed 1500–2000 mg/L. • Increased corrosion risk outside of LSI: sulphates accelerate the deterioration of metals, concrete, and cement surfaces. Damaged and rough surfaces accumulate more biofilm → higher chlorine demand → indirectly more chloramine formation and stronger odor.
How to fix the smell and AVOID contributing to It
No need to dump chemicals blindly. Follow these steps:
1. Test the Water
Measure key parameters: • Free Chlorine • Total Chlorine • Stabilizer (CYA) • Total Dissolved Solids (TDS) • Sulphate level
High chloramine levels require adjustment. Elevated TDS can reduce disinfection efficiency and affect automatic control systems. High sulphate levels increase chlorine demand and accelerate surface deterioration, indirectly raising the risk of odor.
2. Shock the Pool
Use liquid chlorine, considering your CYA level: • Low CYA (<30 ppm): light shock is usually enough. • Medium CYA (30–50 ppm): raise free chlorine to 20–40% of your CYA. • High CYA (>50 ppm): chlorine is less effective; partial water replacement may be needed before shocking.
Apply in the evening, allow circulation for 24–48 hours, and keep swimmers out until chlorine reaches safe levels.
If the disinfection system is stable and automated, shock treatment is needed only in rare cases, such as heavy use or a chemical imbalance.
3. Prevent Future Problems • Shower before swimming • Remove debris from the surface daily • Vacuum the pool weekly • Change water as needed • Monitor the chemical balance of the water • Consider UV or ozone systems to help reduce chlorine demand • Use enzyme products to break down oils and organic matter
If the smell persists, it could indicate algae or buildup in pipes or the filter — a professional inspection is recommended.
A fresh, odor-free pool isn’t magic, and “more chlorine = cleaner” is a misconception. It requires stable chemistry, a properly managed automated system, and regular monitoring. Then the water stays clean, clear, and safe for swimmers and equipment.