Bromine basics: bromine is a popular choice when it comes to hot water sanitization. Here are some tips on working with chlorine's halogen cousin.(Tech Talk)

Once considered an alternative sanitizer, bromine is now commonly used in commercial aquatics applications. Here's a look at the characteristics that make bromine a popular spa sanitizer and the variables you need to consider when testing for its presence.

When bromine is added to water, it forms the sanitizer and oxidizer hypobromous acid (HOBr). Like hypochlorous acid, hypobromous acid reacts with contaminants in water resulting in combined bromine (bromamines). Compared to chloramines, bromamines are less irritating to skin and eyes and create less odor. There's no need to eliminate bromamines with a "breakpoint" procedure; they rapidly decompose.

After its sanitizing and oxidizing power is depleted, hypobromous acid ultimately reverts to bromide ions (Br-). The concentration of these ions in water is called the bromide "bank," and it has no further sanitizing potential.

However, a bromide ion can be reactivated to hypobromous acid by an oxidizer like chlorine or potassium monopersulfate. If chlorine is added to a spa previously sanitized with bromine, it will only regenerate the established bromide bank. Thus, the spa must be completely drained and refilled with fresh water in order to convert from bromine to chlorine sanitizer.

Spas differ from pools in two respects: higher temperatures and smaller volumes. Bromine remains effective at the increased temperatures found in spas, and its efficiency is practically independent of pH (a definite benefit in spas, where pH can fluctuate due to the smaller volume).

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For example, at a pH of 7.5, 94 percent of bromine versus 50 percent of chlorine is in the killing form. While at a pH of 8.0, bromine is at 83 percent efficiency and chlorine is only at 22 percent.