5 min read · TopTubs Lincolnshire Ltd
Different smells from your hot tub mean different things — and most of them are telling you something specific about your water chemistry. Here's a guide to the most common hot tub odours and what to do about them.
Counterintuitively, a strong chlorine smell usually means your chlorine levels are too low, not too high. The smell comes from chloramines — the compound formed when chlorine reacts with organic waste (sweat, body oils, cosmetics). Chloramines are less effective as sanitisers and are the main cause of eye and skin irritation too.
Fix: Shock the tub with a heavy dose of chlorine or non-chlorine shock to break down the chloramines. Remove the cover and run the jets for 30 minutes to allow off-gassing. The smell should diminish significantly.
A musty smell suggests biofilm — a colony of bacteria protected by a slimy layer that forms inside your pipes, jets and equipment. Biofilm is resistant to normal sanitiser levels and requires a targeted flush.
Fix: Add a hot tub pipe flush product (such as Ahh-Some or Swirl Away) and run the jets for 30–60 minutes. You'll often see brown or grey gunk coming out of the jets — that's the biofilm being expelled. Drain and refill after.
Biofilm is the reason we recommend a pipe flush every time you drain your tub, not just when you notice a smell.
The sulphur smell is caused by hydrogen sulphide, produced by sulphur-reducing bacteria. This is a sign of severe bacterial contamination — the water is unsafe to use immediately.
Fix: Do not use the tub. Superchlorinate, run jets for an hour, then drain, scrub, and refill. This smell doesn't improve with routine treatment.
An unusual sweet or chemical smell sometimes comes from algaecide products or specific chemical combinations. It's generally harmless but worth investigating if you've recently changed chemicals or added something new.
A burning smell from the equipment compartment is serious. Switch the tub off at the isolator immediately and call us — do not use the tub until it has been inspected. Electrical faults in wet environments are dangerous.
Never ignore a burning smell from a hot tub. Switch off at the mains and call a professional before using it again.
If the smell is present even without the jets running, the source is the water itself. Smell with jets on tends to come from the pipes. Both need addressing but the treatment differs — pipe flush for jet-related smells, chemical rebalance or drain for water smells.