A hot tub should not have a strong, unpleasant or stale smell. If your spa smells strongly of chemicals, musty, damp, dirty or eggy, it is a sign that the water or equipment needs checking.
A smell does not always mean there is too much chlorine or bromine. In many cases, it can mean the sanitiser is struggling, the water is overloaded, the filter needs cleaning, or the cover and pipework need attention.
The best first step is to test the water and check the basics before adding more products.
What does a hot tub smell usually mean?
An unusual smell usually means something in the water is out of balance, overloaded or not being cleaned effectively.
Common causes include low chlorine or bromine, used-up sanitiser reacting with contaminants, pH or alkalinity outside the recommended range, dirty filters, old water, body products, a damp cover, or build-up in pipework and around the waterline.
The type of smell can give clues, but it should not be used as the only way to diagnose the problem.
Why does my hot tub smell strongly of chlorine?
A strong “chlorine” smell does not always mean there is too much chlorine.
It can happen when sanitiser has been working hard and reacting with sweat, oils and other contaminants. This can make the water smell harsher than expected, especially after heavy use.
Start by testing the water. Check sanitiser, pH and alkalinity before deciding what to do next. Do not simply add more chemicals based on smell alone. Follow your product labels and retest before using the hot tub.
Why does my hot tub smell musty or stale?
A musty, damp or stale smell can be linked to poor filtration, old water, a dirty filter or a cover that needs cleaning.
It may also happen if the hot tub has not been used for a while, if circulation has been poor, or if water has sat around the cover, headrests or waterline.
Check sanitiser, pH, alkalinity, filter condition, waterline build-up, cover condition and whether the water is old or difficult to balance. If the smell keeps returning after testing and cleaning, the water may need replacing.
What should I check first?
1. Test your sanitiser level
Start with chlorine or bromine. If sanitiser is low, the water may not be properly controlling contaminants. This can lead to smells, cloudy water or other water problems.
Use your normal test strips, digital tester or water testing method. If you use SpaWise, log your reading so you can see what needs checking next. Always follow the instructions on your chemical product label and retest before using the hot tub.
2. Check pH and alkalinity
pH and alkalinity affect how stable the water is and how well sanitiser can work. If they are outside the recommended range, the water can become harder to manage and smells may return.
3. Check the filter
A dirty or overloaded filter can contribute to unpleasant smells. Your filter removes fine particles, oils and debris. If it is clogged or overdue a clean, it may not remove enough of the material that feeds water problems.
Remove the filter and check whether it needs rinsing, cleaning or replacing.
4. Check the cover and waterline
Hot tub smells do not always come from the water alone. The underside of the cover, headrests, waterline and shell edges can hold moisture, oils and residue. Wipe around the waterline and check the cover for trapped moisture or build-up.
Can body products make a hot tub smell?
Yes. Sun cream, body lotion, fake tan, make-up, deodorant, hair products and detergent in swimwear can build up in hot tub water. Warm water and jets spread these residues through the water. Showering before use and rinsing swimwear well can help reduce the build-up.
Should I use fragrance to cover the smell?
No. Fragrance may hide a smell for a short time, but it does not fix the cause. If the water smells unpleasant, test the water and check the filter, cover and waterline. Deal with the cause first rather than masking the smell.
Can I use my hot tub if it smells bad?
An unpleasant smell should be treated as a sign to stop and check the water before bathing.
Do not use the hot tub if sanitiser is low, the smell is strong, stale, musty or unpleasant, the water is cloudy, green or slimy, the filter is dirty or blocked, or you are unsure whether the water is properly sanitised.
Test the water, check the filter and cover, correct the underlying issue according to your product labels, allow the water to circulate, and retest before use.
If in doubt, do not use the hot tub until the water has been checked and the readings are back within the recommended range.
When should I drain and refill?
If a smell keeps coming back after testing, balancing and cleaning, the water may be overloaded.
Consider draining, cleaning and refilling if the water is old, the smell returns quickly, the water is cloudy or difficult to balance, the filter has been cleaned but the smell remains, there is visible waterline build-up, or you are unsure what caused the issue.
Fresh water may be more sensible than continuing to adjust water that is already carrying too much build-up.
Quick checklist: smelly hot tub water
- Test chlorine or bromine.
- Test pH and alkalinity.
- Check and clean the filter.
- Wipe the waterline.
- Check the underside of the cover.
- Think about recent use and body products.
- Avoid masking the smell with fragrance.
- Retest before using the hot tub.
- Drain and refill if the smell keeps returning.