What Does It Mean When Pool Water Smells Fishy or Musty?

Short answer: Treat a fishy or musty smell as organic contamination, weak disinfection, or a dirty filter. Measure, clean, and filter first — dose afterward.

For most people, a bad smell is a strong warning sign. They often ask whether adding chlorine is enough. In reality, you need to find out whether the smell comes from the water, filter, skimmer, or the cover.

How to Recognize the Cause

• The smell worsens after uncovering the pool.
• The filter or skimmer is clogged with organic matter.
• Chlorine is low, or conversely the water smells strongly of chloramines.
• The water can be clear and still smell.

What to Do Now

1. Remove leaves and debris.
2. Clean the skimmer, baskets, and filter.
3. Measure pH and disinfectant.
4. Adjust the pH.
5. Depending on the test, perform shock oxidation and let the filtration run.

When It’s Better Not to Bathe

• When the water smells musty.
• When disinfectant isn’t measurable.
• When the water is cloudy or slimy.

Prevention

• Don’t leave organic matter in the skimmer.
• Clean the surface right after a storm.
• Ventilate a covered pool regularly.
• Keep disinfectant levels stable.

When to Call a Service Technician

Call a service technician if the smell comes from the equipment or filtration, or returns after a full cleaning.

FAQ

Is adding chlorine enough?

Only if the pH and filtration make sense. Chlorine in a clogged system often just masks the problem.

Can clear water smell too?

Yes. Clear water isn’t necessarily hygienically fine if it isn’t measured and the disinfection isn’t working.

Sources

• CDC – water testing in home pools and hot tubs
• CDC – hot tub safety
• Modrá střecha – pool discussion forum
• Reddit r/hottub – common questions from hot tub owners
• Trouble Free Pool – community advice on pool water
• ALBIXON – most common pool water problems
• ARIVA – green pool water
• Upravvodu.cz – pool water problems
• Monitoring Laboratory – hot tub water treatment