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Chlorine Versus Bromine

What’s your preference for hot tub water care?

Everyone has a preference in competitive markets: Burger King versus McDonald’s, Walmart versus Amazon and even the hot tubs in a showroom are the brand dealers prefer over others. And in the world of chlorine versus bromine, the competition is likewise fierce.

What’s the difference?

You can’t have a good matchup without a little back-story on the competitors. Terry Arko, product training and content manager at HASA, has 40 years in the industry, has written more than 100 articles on pool and spa water chemistry, presents on the subject at trade shows, is a certified instructor with the the Pool & Hot Tub Alliance and serves on its Recreational Water Quality Committee.

Arko says chlorine and bromine are both halogens, or formed from salt — chlorine from sodium chloride and bromine from sodium bromide. Both are FDA approved disinfectants that kill disease-causing organisms, oxidize nonliving contaminants and leave protective residual in the water. Chlorine’s primary killing agent is hypochlorous acid (HOCl) and bromine’s is hypobromous acid (HOBr).

The main difference between chlorine and bromine is the percentage of killing agent in the water based upon the water’s pH, Arko explains. “For example, at a pH of 8.0, there would only be 24% active HOCl in the water, but a pH of 7.2 has 66% HOCl in the water,” Arko says. “The production of the killing agent for bromine HOBr is nowhere near as contingent on pH as with chlorine. For example, a pH of 8.0 would be 83% HOBr and a pH of 7.2 has 96% HOBr in the water.”

Chlorine requires the addition of 30 to 50 ppm of cyanuric acid (CYA), otherwise up to 50% of residual chlorine is destroyed by UV light from the sun in less than an hour, Arko says. Sodium bromide requires an oxidizer — potassium monopersulfate (MPS) — to create active bromine. Sunlight destroys bromine at the same rate as chlorine in UV light, but CYA will not prevent its degradation. “Chlorine consumption and ability to hold residual becomes compromised at water temperatures above 85 degrees,” Arko says. “Bromine has the ability to hold a residual at water temperatures up to 104 degrees.”

Which side are you on?

John Bokor, regional sales manager for Haviland, says the choice between chlorine and bromine depends on the application. “A lot of times, in residential outdoor applications, the preferred method [of sanitizing] would be some type of stabilized chlorine,” he says. “As the pH of the water changes, chlorine can either become hyperactive or slow working. Bromine, on the other hand, has a much wider range so the consumer can actually make some mistakes and still have a safe swimming environment.”

Lance Fitzsimmons, who is in charge of sales and technical support at ControlOMatic (manufacturers of salt water chlorinators in Grass Valley, California) and a Certified Pool/Spa Operator Instructor, prefers chlorine. “In hot tubs, bromine is much more popular due to its stability in heat,” Fitzsimmons says. “Since the introduction of chlorine generators for hot tubs, however, chlorine has become much more viable and effective in hot tubs.”

Ninety percent of the repair calls for heater and pump failure received by California Custom Hot Tubs (CCHTS) in Sonoma are due to customers using bromine tablets, according to president and CEO, Thomas Rosander. “The bromine is acidic and acidic water is very clear, so people think the water is fine from just a visual inspection,” he says. “They forget how important pH is to the health of the water and the tub equipment.” CCHTS encourages customers to use dichlor and a nonchlorine shock weekly.

“I like bromine,” says Paolo Benedetti, CEO of Aquatic Technology Pool & Spa in Morgan Hill, California. While he knows bromine is more expensive than chlorine, “Once chlorine combines with contaminates and forms chloramines, it ceases to be an active sanitizer. However, once bromine combines with contaminants and forms bromamines, it continues to be an active sanitizer.”

Ken Leonard, president of Carefree Spas in Indianapolis, says the company was strictly bromine for 12 years, but the last 18 years they have recommended granulated chlorine to customers. For him, it isn’t whether one is better over the other, but the fact that bromine caused his customers to form bad habits using too much — adding more and more without looking at water chemistry.

“We switched people over to granulated chlorine and teach them what to do and when to do it,” Leonard says. “It keeps the customer involved, and 80% of our chemical questions went away when we switched from a bromine-based company to a chlorine-based company. It just got them to focus differently, plain and simple.”

However, Theodora Sergiou, vice president and COO of Nicholas Pools in Toms River, New Jersey, recommends bromine for hot tubs. “Since a hot tub has a small amount of water, it requires a higher concentration of chlorine [than bromine does] to effectively sanitize the water,” she says. “Bromine lasts longer in hot water. Also, chlorine has an odor to it, so [we don’t use it] for spas since a spa has to be covered to keep the heat in and will not allow the smell to dissipate.”

Bokor advises treating the recommended choice like a prescription based upon how the water is used. “You have to examine and take in all the aspects of what is going on,” he says. “From bather load — how many people are using this thing at a time — to the environment that it’s in — indoors, outdoors, exposed or covered. All of those things come into play.”

Arko agrees. “For [outdoor] swimming pools, chlorine is the preferred choice because it is effective, economical, and is able to be stabilized by the use of CYA to prevent degradation from UV sunlight,” he says. “For spas [and indoor pools], bromine would be a better choice as it disinfects over broad pH ranges and has better efficacy at high temperatures.”

“Both have a place in the industry,” Bokor says. “Sometimes one method is preferred over the other, but both are applicable.”

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