Bromine is a chlorine alternative, but it's used more often in hot tubs than in swimming pools for three reasons: It costs more than chlorine; it can't be stabilized as easily; it works better in hot water. Bromine is chemically similar to chlorine, and like chlorine, it can burn skin and bleach bathing suits if the concentration is too high. Because it's volatile, the easiest way to lower bromine levels is to let the water outgas. You can also lower the concentration by adding more water or by neutralizing the bromine. You neutralize by adding sodium thiosulfate to the water.
Disinfecting With Bromine
Located just under chlorine in the periodic table of the elements, bromine is one of the halogens, with a valency of 1. It is highly reactive, and when added to water, it forms hypobromous acid (HOBr) in the same way that chlorine forms hypochloric acid (HOCl). Both acids dissociate to produce ions that combine with ammonia compounds to form amines, but bromamines -- unlike chloramines -- can still function as a sanitizer. This fact, together with the fact that dissociation of HOBr is less affected by pH than the dissociation of HOCl, probably makes bromine a better sanitizer than chlorine, on the whole.
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The main problem with bromine -- other than its cost -- is that it is unaffected by the stabilizer that protects chlorine from degradation by sunlight. Consequently, it doesn't last long in an open pool, and you have to keep adding more. Because bromine is more stable at high temperatures than chlorine, it is more useful for sanitizing spas and hot tubs -- which generally have covers -- than open pools.
Can Bromine Levels Be Too High?
In its pure form, bromine is corrosive and smelly. In fact, its name comes from the Greek word "bromos," meaning "stink." Although bromamines are not as odorous as chloramines, a high concentration of bromine in a pool or hot tub produces a discernible, disagreeable odor, especially after the water sits undisturbed for a length of time. Add to that the possibility of watery eyes, itchy skin and "bromine rash" on your thighs and midriff, as well as the corrosion of metals in the pool and the circulation system, and you can appreciate the need to keep bromine levels within the safe range of 2 to 4 parts per million.
Testing Bromine Levels
You can use the chlorine tester in your regular pool test kit to check the bromine level. Some kits include a scale to indicate the bromine level, but if yours doesn't, simply multiply the number on the free chlorine scale by 2.25 to determine the bromine level.
Lowering Bromine Levels
Bromine is volatile and quickly evaporates from the surface of a pool or hot tub, especially when the water is exposed to sunlight. Consequently, the easiest way to lower bromine levels is to simply wait for the evaporation to happen. If you have a hot tub, leave it uncovered, and run the circulation pump to speed up the process.
If you're in a hurry to swim or soak, and don't want to wait for the pool or tub to outgas, you could dilute the water to lower the bromine concentration, but this is usually impractical. Instead, add sodium thiosulfate to the water to neutralize the bromine. Although each product is different and comes with its own instructions for use, you generally need to add an ounce or two per 10,000 gallons to lower the bromine level by 1 ppm.
For the fastest neutralizing action, stir the granules into a container of water until they dissolve, and then pour the water into the skimmer and run the circulation pump.