Bromine tablets stay effective in hot water, hold a steadier 4-6 mg/l residual with less dosing and are kinder on skin - why so many UK tubs use them.
Bromine tablets are so widely used in UK hot tubs because they solve chlorine's two big weaknesses in spa conditions: bromine keeps killing bacteria at hot tub temperatures and across a much wider pH range, and slow-dissolving tablets in a floating dispenser hold a steady 4–6 mg/l residual for days with minimal effort. They are also gentler on skin and produce far less of the sharp "chemical" smell, which is why bathers with sensitive skin often switch and stay switched.
A hot tub at 37–40°C is a hostile place for chlorine: heat drives it off quickly and its killing power falls away sharply once pH drifts above 7.6. Bromine is far more forgiving on both counts – it remains an effective sanitiser across a wider pH band and does not disappear as fast in hot, aerated water. In a small vessel where two bathers can swing the chemistry in a single soak, that tolerance is exactly what you want. The full comparison is in our guide to chlorine vs bromine for UK hot tubs.
The tablet format is the other half of the appeal. 20g bromine tablets dissolve slowly in a floating dispenser, releasing sanitiser continuously between soaks. Instead of dosing granules after every bathe, you top up the dispenser roughly weekly, adjust its vents to hold the reading at 4–6 mg/l, and confirm with test strips two to three times a week. There is another quiet advantage: used bromine does not simply vanish. Shocking the water with a non-chlorine shock reactivates part of the spent bromide back into working sanitiser, so the residual is easier to keep stable week after week. See how bromine tablets work in hot tub water for the chemistry.
Chlorine's waste products – chloramines – cause the stinging eyes, itchy skin and swimming-pool smell people blame on "too much chlorine". Bromine's equivalent compounds, bramines, remain active sanitisers and produce much less odour and irritation. For families who use the tub often, or anyone with sensitive skin or a sensitivity to chlorine-based products, that comfort difference is usually the deciding factor.
Bromine is not automatically the right answer. Tablets cost a little more than chlorine granules, work out slower to establish a residual on a fresh fill (a bromine starter kit with granules gets the bank started quickly), and bromine cannot be stabilised against sunlight, so an uncovered tub in summer loses it faster. Switching between sanitisers also needs care – if you are moving over from chlorine, follow the steps in switching from chlorine to bromine rather than mixing products. Whichever you choose, keep bromine at 4–6 mg/l (or free chlorine at 3–5 mg/l), pH at 7.2–7.6 and total alkalinity at 80–120 ppm.
Bromine stays effective at hot tub temperatures and across a wider pH range than chlorine, holds a steadier residual in a floating dispenser, and produces less odour and skin irritation. Chlorine still suits owners who want a cheaper, faster-acting sanitiser.
Keep bromine at 4-6 mg/l, tested two to three times a week with test strips, alongside pH at 7.2-7.6 and total alkalinity at 80-120 ppm.
Top up the floating dispenser roughly once a week as the tablets dissolve, then open or close its vents to hold the reading at 4-6 mg/l. Usage, temperature and bather load all affect how quickly the tablets are consumed.
Many bathers find bromine noticeably gentler. Its by-products cause less of the stinging eyes, itching and strong smell associated with chloramines, which is why bathers with sensitive skin often prefer bromine-sanitised tubs.