Hot tub bromine guide
Updated October 2026
Bromine is a popular hot tub sanitiser because it’s gentle on the nose and holds up well in hot water. Here’s how to set it up, what levels to aim for, and how to keep it working.
Bromine levels to aim for
| Test | Aim for | If it’s off |
|---|---|---|
| Bromine | 3 to 5 mg/l (ppm) | Low: adjust the dispenser or add granules. High: leave the cover off and don’t use the tub until it drops. |
| pH | 7.2 to 7.6 | High pH makes water cloudy and scale-forming. Low pH makes it corrosive and irritating. |
| Total alkalinity | 80 to 120 mg/l | Correct alkalinity first. It holds the pH steady. |
Running a holiday let? Business use has its own ranges and testing routine under HSG282.
Setting up a fresh fill
- Fill the tub and balance the alkalinity and pH.
- Add a bromide booster (sodium bromide). This builds the “bromide bank” that bromine works from.
- Shock with a non-chlorine shock to turn the bromide into active bromine.
- Put bromine tablets in a floating dispenser or the tub’s inline feeder.
- Test daily for the first week and adjust the dispenser setting until the level stays in range.
Bromine tablets dissolve slowly, so the dispenser setting is what controls the level. Granules work faster when you need a quick boost.
Why bromine needs shocking
When bromine kills bacteria and breaks down sweat and oils, it turns back into bromide, which doesn’t sanitise. A non-chlorine shock (potassium monopersulfate) burns off the waste and turns that bromide back into active bromine.
- Shock once a week, and after a busy session.
- Run the jets with the cover off while it mixes.
- Test before anyone gets in, and follow the label for how long to wait.
Never mix chemicals or add them together. Add each one separately to the water, with the pump running.
Common bromine problems
- Bromine reads low
- Check the dispenser isn’t empty or turned down. If the tub has been in use for months, the water may need changing.
- Cloudy water
- Check the pH and alkalinity, clean the filters, then shock.
- Itchy skin or sore eyes
- Usually the bromine or pH is too high or too low. Retest and correct before using it.
Bromide and dissolved waste build up over time, and shocking won’t remove them. Drain, clean and refill the tub regularly. Your manual gives a guide to how often, depending on use.
Switching to chlorine? Drain and refill first. Chlorine added to bromide-rich water just turns into bromine.
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