photo of boy with swimming goggles

Scientific foundation for this article was provided by Zach Hansen, technical services engineer at BioLab. Mr. Hansen has a Bachelor of Science in Chemical Engineering from Auburn University and an MBA from Georgia State.

Chlorine for pools, bromine for spas. That’s the conventional wisdom for sanitizing, but like most conventional wisdom, there are circumstances when it’s not so wise.

Over many decades, chlorine has been tried and found to be a true and lethal germ-killer and waste oxidizer in outdoor pools, but it’s sister halogen, bromine, makes a good case for use in an enclosed space. Mostly, that argument boils down to the fact that bromamines (a major by-product of bromine pool chemistry) are a lot easier to deal with than their counterpart, chloramines, especially in commercial pools with large bather loads.

Shocking procedures

There are no doubts about chlorine’s ability to kill and oxidize pool invaders. The halogen’s problems begin after it’s done its work.

Once chlorine has reacted with another molecule and become combined chlorine (chloramine), it becomes quite feeble as a sanitizer. But when bromine reacts and becomes a bromamine molecule, it retains its sanitizing efficacy. Bromamines floating around in the water will be able to attack and kill bacteria just about as effectively and quickly as either free chlorine or free bromine.

So while bromamines are a positive good in pool water, chloramines pose a problem in any pool. They build up over time and must be eradicated through breakpoint oxidation. The standard practice in the industry is to dump in a large amount of chlorine to shock the pool, usually in a 10-to-1 ratio of free chlorine to combined chlorine.


Name: Chlorine Atomic number: 17 Atomic weight: 35.453 Melting point: -150.7 °F Boiling point: -29.27 °F Standard state: Gas at 298 K (76 °F) Group name: Halogen Group in periodic table: 17 Color: Yellowish green Classification: Non-metallic

But there are problems with this procedure (beyond the obvious expense and hassle), especially when performed indoors and at a magnitude necessary to treat a commercial pool. Large doses of shock react with organic contaminants to form chloramines on a grand scale.

Even without the addition of shock, chloramines are volatile and have a strong tendency to “gas off” and become airborne. This is a problem in indoor pools, where comparative lack of ventilation holds concentrations of airborne chloramines within the building and close to the waterline.

Most people are familiar with the odor problem chloramines present — what is often described as a “chlorine smell.” That is simply an indoor chloramine cloud being sucked into one’s olfactory and respiratory system.

This is even more of a problem for swimmers who, as they churn through the lanes, pant along with their mouths just above the surface where chloramine concentration is heaviest.

Some are more sensitive to these chemicals than others, but intuition — supported by the general protest of the eyes, lungs and mucus membranes — suggests airborne chloramines cannot be good for us. The scientific community has reached no definitive conclusion on the matter, and research continues on the topic.

Bromamines, on the other hand, are much less likely to become airborne. They do not gas off, but remain in liquid state, held within the volume of pool water, where they actually do some good.


Name: Bromine Atomic number: 35 Atomic weight: 79.904 Melting point: 19 °F Boiling point: 138 °F Standard state: Liquid at 298 K (76 °F) Group name: Halogen Color: Red-brown, metallic luster when solid Classification: Non-metallic

A third, considerable problem with indoor pool chloramines is they attack the building. Owners of indoor pools with stainless steel fittings will be familiar with the severe corrosion that results when chloramine-filled vapors condense on cool steel. This chloride-rich mixture will eat away at almost any steel component of the pool’s surrounding structure, be it window frames, door hardware, ductwork or HVAC equipment.

So to summarize the pro-bromine argument, bromine pools do not need to be shocked to treat combined bromine (a positive contributor to pool health) in the way that chlorine pools must be shocked to treat combined chlorine (a bad actor, both in and out of the pool). The chlorine shocking procedure has costs, both monetary and in terms of the pool environment. And chloramines tend to go airborne, where they are a general nuisance.

That Unstable Feeling

Of course, chlorine has some great advantages. (It didn’t become the king of pool sanitizers for nothing.) Stability in the sun is one of them.

Bromine can’t be stabilized the way chlorine is stabilized with cyanuric acid. So in an outdoor pool environment, bromine is highly susceptible to degradation by UV from the sun. For that reason, bromine in an outdoor pool would be an expensive proposition, as it would have to be added quite frequently. Indoors, however, that objection is largely removed.

Another nice thing about chlorine is that it can be applied conveniently. It comes in handy tablets, which can be placed in the skimmer and released at a controlled rate.

You can tablet bromine, too, but it’s much slower to dissolve, so you can’t typically apply it through a skimmer. You need special equipment to apply bromine in pools, which means upfront expense, whereas with chlorine, you can apply with tablets or use granular chlorine, like dichlor or cal-hypo, which will dissolve rapidly.

With chlorine you have both options — a slow-dissolving, slow-release sanitizer product or a quick-release shock product. (Both chlorine and bromine can be applied with automatic feeders.)

Bromine is also a less powerful oxidizer than chlorine, so when you’re using it to break down bather waste in a pool, it’s not quite as effective as chlorine. Basically, that means the homeowner or service pro must stay on top of things or he’ll be buying oxidizer — either monopersulfate or chlorine shock — to eliminate waste buildup. (Yes, you can use chlorine shock in a bromine pool or spa, subject to certain caveats.)

The biggest obstacle to bromine use in pools, however, is probably experience. Chlorine has long been the most prevalent sanitizer in the pool industry, and most pool managers, whether professional or amateur, are trained in the use of chlorine as a sanitizer.

It’s an educational barrier, however, that often leads to the selection of chlorine as the sanitizer for a new indoor pool without the consideration of the benefits of bromine.

Bromine is certainly as effective as chlorine when it comes to killing bacteria in recreational water, but there are nuances to the question of which is better. Chlorine is cheaper to buy, holds up better under the hot sun, and the technology for its use in pools is more developed and generally better understood. But, especially for the indoor pools, bromine offers distinct advantages based on its relatively benign and even helpful by products. It is left for the pool manager or builder to analyze which advantages are most important and create the best outcome for a particular pool.

Comments or thoughts on this article? Please e-mail [email protected].

Scott Webb is Executive Editor of AQUA Magazine.
Anonymous 5 days ago
Scott, great article, I must have missed it when it first came out, but thanks to the AQUA email letter it caught my attention. It is nice to see some educated facts shared about the benefits of bromine in our industry!
Charles Kozicky Monday, 12 August 2013
Both chlorine and bromine have problems as we all know. The product I have does not play well with bromine, so I'll give attention to chlorine and why it needs help. # 1. As bromine and chlorine are, sunlight and heat degrade their chemical compounds. # 2. Chlorine is great until people enter the pool and bring organic material like suntan lotion, sun block, urine, feces, and other things. # 3. once these organics enter the water they begin to eliminate chlorine and it's effectiveness to kill algae and bacteria while causing pH levels to become unsafe which is critical for chlorine to do it's job. My product helps stabilize the pH levels and helps chlorine kill algae and bacteria with low levels of free available chlorine from .05 to 1.5 ppm.. Go to to learn more.
Chlorine added to water is a fast and furious and is quickly gone with the rapid oxidiser that it produces. Bromine is slow killer, a poor oxidiser, and combines with nitrogenous waste to produce a much more dirty compound that can linger , producing a sickly mess, biologically. That sickly mess is , your skin. Bromine made its appearance on the hot tub scene as an answer to hot tub dealers that were having difficulty selling soft product that was being traditionally used in the larger water volume swimming pool market. That product was and is chlorine. The bleaching agent , hypochlorous acid is almost an instant killer and oxidiser that will clear away biological waste providing it is used in a dominant quantity. That is why a free residual residual needs to be kept up , always , in a dominant way , especially when using bromine..... So why would the industry use bromine.... Because the low water volume hot tub business needs to make ends meet....
I am compelled to pose two questions. We are all aware that halogen compounds are carcinogenic, but how do bromamines compare to chloramines? I've heard the former are much more carcinogenic than the latter. Also, is it not true that chlorine is a wider spectrum sanitizer? I've heard of some type of black growth (be it a fungus or algae) that will flourish in a brominated hot tub, and the prescription to alleviate the problem is to use chlorine.
Art, allow me to correct a few of your assumptions here. Neither bromamines nor chloramines are carcinogenic. Their respective "-ate" ions, such as Bromate Ion, in very large concentrations, has been found to be possibly carcinogenic, according to the EPA. But under normal circumstances, these "-ate" ions will not be present in the water (otherwise the EPA would not allow the use of bromine or chlorine). You can Google the EPA reports on this subject from 2010 and 2013. Secondly, Bromine is not only an equal sanitizer (same spectrum) as Chlorine, but since it is not effected so easily by pH fluctuations, nor does it gas off to vapor until 140 degrees, and since the bromamines are still effective sanitizers after the initial round of cleaning after being introduced, Bromine is in fact far superior as an effective sanitizer. It is the clear choice for hot tubs because of the hotter water, and would be the clear choice for swimming pools if chlorine wasn't so much less expensive (although an argument can be made that chlorine is more expensive since you have to use more of it). A salt water system that uses sodium bromide salt instead of sodium chloride salt, producing bromine instead of chlorine is, ultimately, the best choice hands down.
I run my swim spa on bromine and have operated outdoor residential pools on bromine. I troubleshoot many issues with bromine...but the common denominator is not a problem with is operator error. I have seen bromine spas that were not tested properly...due to a lack of education, where the operator thought the pH was high, when it was actually about 5. The problems that I see with bromine have nothing to do with the product and everything to do with the education and procedures of the operator. I have also heard of many cases of rash from pseudomonas from poorly operated chlorine's not the chlorines fault, either...just poor education and operation. The water in our swim spa is not harsh, by any stretch of the imagination...we have family members and babies with sensitive skin in the water with no issues.i have spent hours and hours in an outdoor pool/spa on bromine with no one having a harsh fact les eye burn and irritation than from the average backyard pool...again...I believe those are operator error issues in most cases. I also agree with Ed of the early "problems" with bromine...was sales and marketing types telling people they didn't need to oxidize the pool or spa on bromine...wrong. Maybe not as much, or for the same reasons as chlorine, but the water needs to be oxidized...I still like ozone...Asa it was mentioned in the article...all of the products have their place...finding the right combination for your pool and situation is the key.
Well said!!! It really is just a problem with general ignorance where bromine is concerned.
Scott, Nice comparison of chlorine and bromine! I would not go as far as to say "bromamines are a positive good in pool water", as stated in the article, but I agree completely that they are much less objectionable than chloramine, primarily because they are less stable (more reactive) and less volatile. Pools that are sanitized with bromine most certainly do need oxidation, or if not oxidation, they need a mechanism to remove organic contaminants and minimize bromamine formation. Because it is likely that "bromamines" are the cause of the swimmer irritation and skin issues mentioned in previous replies, much more so than free bromine. Finally, while I agree that "experience" plays a significant role, having the right information is equally as important. In my opinion the real challenge when using bromine is understanding the impact, and managing the buildup, of inert bromide ion, which is inherently done to some extent in spas/hot tubs, but not so much in pools.
While I agree that Bromine is a great choice for indoor commercial pools and spas, as another person pointed out, Bromine is very harsh on the skin - the reason for the hot tub fragrance/softening lines. I teach swimming at a YMCA with an indoor Chlorine pool - the air handling system is key, as well as the fact that a CPO is running that pool (she maintains balance and great air quality, even in an aging indoor pool). There is never a "Chlorine smell" at that pool. I can walk into a hotel, and tell you from the lobby if the pool is ok to even consider, due to the smell. Great article, chemistry wise, but missing a few facts about Bromine.
V. John Truglio Tuesday, 25 June 2013
Great article Scott ... much validity with use of bromine for indoor pools / spas ... As a CPO instructor, I stress the chloramine / bromamine factor as an extremely important part of the pool water chemistry in my classes. John
Bromine is great! It's algicidal at only 0.2 PPM. I totally recommend it for indoor pool use.
bromine is a weak sister to Chlorine and can kill bacteria , but does not have a good bleaching potential for the wasting of the dead bromine may stick around for a long time , killing biology , but your water will be filled with phenols and other nitrogenous waste that not only gives a bad vue but also is a nutrient to any new biology.....
really Patrick? I have about 60,000 customers in North America and Europe running their hot tubs and swim spas on pure bromine salt water systems FOR NEARLY 20 YEARS who would refute your statements "bromine is a weak sister" and "your water will be filled with...waste..." etc. Chlorine of any type is never used with our systems. I'm afraid these blanket statements just are not accurate. You can learn more here: