A bromine tablet is a slow dissolving sanitiser tablet used to keep hot tub water clean. It releases bromine into the water over time, helping maintain a steady sanitiser level between top ups and routine water care checks.
For most UK hot tub owners, bromine tablets are used as part of a simple weekly routine. They are usually placed in a floating dispenser or the spa's tablet feeder so the dose can dissolve gradually, rather than being added loose into the water.
Before adding a bromine tablet, test the water and make sure pH is in the correct range for your spa care routine. Then place the tablets into a floating dispenser or feeder and adjust the openings so they dissolve at a steady rate. The exact number needed will vary by spa size, water temperature and how often the hot tub is used.
Check the water regularly and top up the dispenser before it runs empty. If the hot tub has had heavy use, cloudy water or a fresh refill, you may also need separate water balance products or a shock treatment as part of normal maintenance.
Slow-dissolving 20 g bromine tablets for hot tubs and spas. Dropped into a floating dispenser they hold 4-6 ppm bromine for 1-2 weeks per dose, ideal for low-effort weekly maintenance.
Available in 1kg, 2.5kg, 5kg, 10kg, 20kg and 25kg tubs.
Each tablet weighs 20 g, so a standard dose works out at 20-40 g per 1,000 L. Adjust based on bather load and water temperature. Heavy use or hot weather may require an extra tablet or a wider dispenser opening.
Bromochlorodimethylhydantoin (BCDMH) compressed into 20 g slow-release tablets. Each tablet contains at least 60% available halogen and is engineered to dissolve evenly over 1-2 weeks in a dispenser.
BCDMH releases hypobromous acid (HOBr), the active sanitiser, plus a small chlorine activator. The chlorine recycles spent bromide back into active bromine, sustaining the bromine bank with very little product compared to dosing chlorine alone.
Bromine remains active above 38 C, where chlorine is destroyed quickly. The slow-release tablet form hands you a full week of stable sanitiser without daily intervention, the standard professional approach for hot tubs.
Depending on the flow rate and water temperature, the tablets typically last 1-2 weeks before needing replacement.
Yes, these are perfectly safe and effective for inflatable hot tubs when used in a floating dispenser.
As a general rule, use 1-3 tablets per 1000 litres of water, adjusting based on regular testing to maintain 4-6 ppm.
50 tablets at 20 g each, around 4-6 months for a typical 1500 L hot tub.
Yes. Bromine forms fewer skin-irritant by-products than chlorine and is the standard choice for sensitive bathers.
Use only when the salt cell is offline; bromine and salt chlorination are not run together.
Bromochlorodimethylhydantoin (BCDMH) at >= 60% available halogen.
Bromine remains stable above 38 C while chlorine is destroyed quickly. Hot tubs need a sanitiser that survives the heat.
Yes, weekly with Non-Chlorine Shock to clear combined bromine and restore active bromine bank.
Open dispenser; dose Bromine Granules to refresh the bank.
Shock with MPS; ventilate for 30 minutes.
Close dispenser ports; check water temperature is within range.
Bromine handles heat better and is gentler on skin; chlorine is cheaper but burns off faster at hot tub temperatures.
Tablets give slow steady release for low-effort care; granules give fast top-ups when bromine has dropped.
How the three main hot tub sanitiser families compare for everyday use, hot water performance and running cost.
| What matters | Chlorine | Bromine | Chlorine dioxide |
|---|---|---|---|
| Best for | Fast, low-cost everyday sanitising | Hot tubs and spas that want a steadier, milder feel | Deep cleans, biofilm removal and problem water |
| Ideal level | 3 to 5 ppm free chlorine | 4 to 6 ppm total bromine | Used as a clean-up dose, not a daily residual |
| Performance in hot water | Burns off faster at spa temperatures | Stays effective in hot water | Used as a strong clean-up dose, often chosen for biofilm problems |
| pH sensitivity | Works best at pH 7.2 to 7.6 | Effective across a wider pH range | Largely unaffected by pH |
| Odour | Noticeable when chloramines build up | Milder than chlorine | Low odour at normal clean-up doses |
| Typical running cost | Lowest day to day | Slightly dearer than chlorine | More per dose, but only used occasionally |
| ClearSpa products | Stabilised chlorine granules and mini tablets | Bromine tablets 20g and bromine granules | Chlorine dioxide |