Other members of the halogen family – bromine and iodine – are used for treating pool water. New developments in the use of ozone, ultraviolet light, ionization of salts and other chemical compounds continue to provide new challenges and techniques in water treatment.
Although bromine in its elemental form is a liquid, it is not available for swimming pool disinfection in that form. Elementa l bromine is a heavy, dark brown, volatile liquid with fumes that are toxic and irritating to eyes and respiratory tract. For pool sanitation, bromine compounds are sold in two solid forms – a two-part system that uses a bromide salt dissolved in water and activated by addition of a separate oxidizer; and a one-part stick or tablet that contains both bromine and an oxidizer and is dispensed by an erosion-type feeder.
The chemistry of bromine is similar in many respects to the chemistry of chlorine; however, bromine cannot be used for shock treating.
Bromine has a pH of 4.0-4.5. When bromine is added to water and an oxidizer is present, the bromine forms hypobromous acid (HOBR) and bypobromite ions (OBr). Like chlorine, the percentage of each is affected by pH. However, the effect is not as dramatic as it is with chlorine. Like chlorine, bromine combines with organic impurities to form combined bromine or bromamines. However, combined bromine is still an effective sanitizer, and it does not smell. Because of this, bromine is popular for spas.
Potassium iodide (KI) is a white, crystalline chemical that dissolves in water without a precipitate. When activated by the presence of an oxidizer, it is converted to hypoiodious acid (HOI). Iodine does not react with ammonia to produce iodamines; it does not bleach hair or swimming suits, and eye irritation is practically nonexistent. Other chemicals (usually chlorine) must be used in conjunction with iodine to control algae and oxidize organic matter. The sole effect of iodine is to produce bacteria-free water..