Chlorine and bromine are both halogens — chemically similar elements that make effective disinfectants. Both kill bacteria and algae in pool water. But they behave differently in ways that have practical consequences for how a pool needs to be managed, how comfortable the water feels, and how much ongoing chemical input the pool requires.
How they disinfect
Both chlorine and bromine work as disinfectants by forming hypohalous acid in water — hypochlorous acid (HOCl) in the case of chlorine, and hypobromous acid (HOBr) for bromine. These are the active disinfecting species that kill pathogens.
The critical difference is in the pH range at which each remains active. Hypochlorous acid requires the pH to be kept below about 7.8 for chlorine to disinfect effectively. Above that, chlorine shifts into its inactive form and the pool becomes vulnerable.
Hypobromous acid is stable at much higher pH — remaining an effective disinfectant up to around pH 9. This single difference drives almost everything else that distinguishes bromine pools from chlorine pools.
Pool water naturally drifts toward higher pH. With chlorine, you must constantly add acid to hold the pH down to keep the disinfectant working. With bromine, the pool can settle at its natural equilibrium pH — no acid required.
Chloramines — the key practical difference
When chlorine reacts with nitrogen-containing compounds in pool water — urea from urine and sweat, amino acids from skin proteins — it forms chloramines. These compounds are irritating to eyes, skin, and the respiratory tract, and are responsible for the sharp pool smell most people associate with chlorine.
Bromine reacts differently with nitrogen compounds. The reaction products are substantially less irritating, and the characteristic odour and irritation of chloramine pools are absent. A pool running on bromine chemistry does not produce chloramines, which means the water is fundamentally more comfortable to swim in.
Comparison at a glance
| Property | Chlorine | Bromine |
|---|---|---|
| Effective pH range | Up to 7.8 | Up to 9.0 |
| Forms chloramines | ✕ Yes | ✓ No |
| Needs acid to maintain pH | ✕ Constantly | ✓ Rarely |
| Needs water balancing chemicals | ✕ Yes — ongoing | ✓ Minimal |
| Sharp pool odour | ✕ Common | ✓ Absent |
| Eye and skin irritation | ✕ Common | ✓ Minimal |
| Compatible with salt chlorinators | ✓ Yes | ✓ Yes (with Catalyst) |
Why bromine wasn't used in backyard pools until now
Bromine has long been the disinfectant of choice for spas and hot tubs, precisely because it is non-irritating and stable at high temperatures. But the conventional form of bromine — bromine tablets — is expensive to dose at the scale of a full-size swimming pool. This made bromine impractical for everyday residential pools.
Swim Research changes this by using a small dose of sodium bromide as a catalyst. When added to a pool with a salt chlorinator, the catalyst converts the chlorine the chlorinator produces into bromine — cheaply and automatically. The catalyst is not consumed in the process, so only a small top-up twice a year is needed. The result is genuine bromine disinfection at a cost comparable to conventional chlorine maintenance.