What are the differences between bromine and chlorine?
Which of these popular sanitizers is a better choice to use in your swimming pool or hot tub, and why?
Quick answer: Bromine tends to be better for chlorine-sensitive people or used in hotter environments like hot tubs, whereas chlorine is a cheaper and more effective sanitizer in just about every other scenario.
The Differences Between Bromine And Chlorine
Both chlorine and bromine kill bacteria and decontaminate your pool and spa water and they do it in similar ways.
Here are the 9 key differences:
1. Chlorine is a Faster Acting Sanitizer
Chlorine works considerably faster than bromine, so it’s quicker at destroying things like bacteria, algae, and other microorganisms.
This is because chlorine oxidizes contaminants by invading the cell wall and stealing electrons to form combined chlorine. This transfer of electrons happens very quickly.
Bromine, on the other hand, ionizes contaminants by destroying their chemical bonds and forming ions (charged particles). The process of weakening these bonds is much slower in comparison.
If you imagine a contaminant as a metal chain, oxidizing is like cutting and removing some of the links in the chain with pliers, while ionizing is like weakening all the links with a blowtorch until it breaks apart.
Overall, while both are very capable sanitizers, chlorine is the better choice if you need a quick solution to dirty water.
2. Bromine Is a Longer Lasting Sanitizer
Bromine stays in the water longer than chlorine, so it provides protection for a longer time. This just means it requires less frequent involvement to keep your water properly sanitized.
When bromine gets used up in the water, it forms bromamines that continue to fight off contaminants. While bromamine isn’t quite as effective as bromine, it’s still often strong enough to maintain your water for a little while longer.
On the flip side, chlorine produces a byproduct called chloramines which are not only significantly weaker than chlorine but also consume some of your free chlorine as they’re essentially contaminants themselves.
Note: Bromine is also more resistant to UV, which can arguably make it last longer in comparison. However, outdoor pools use stabilized chlorine (paired with cyanuric acid) which is even more resistant than bromine.
3. Chlorine is Cheaper to Use
Chlorine is almost always cheaper than bromine, which means it’s cheaper to use as a residual sanitizer.
Bromine tends to be more expensive than chlorine because it’s not as widely produced or sold, and a lesser demand for the product inherently increases manufacturing costs.
With that being said, while chlorine is more affordable than bromine off the shelf, the cost difference isn’t quite as significant as it appears as bromine lasts considerably longer in the water, resulting in less frequent top-ups.
4. Bromine Causes Less Skin and Eye Irritation
Unless you’re allergic to bromine, it isn’t as aggressive as chlorine on your skin and eyes, which makes for a more comfortable swim or soak.
This is because bromine produces bromamines as a byproduct of sanitation whereas chlorine produces a much harsher byproduct in the form of chloramines (or combined chlorine).
That’s not to say bromine doesn’t cause any skin or eye irritation at all, it just does so to a much lesser degree for most people — which is why it’s a common alternative solution for chlorine-sensitive people.
While bromine is gentler on the human body, however, washing it off can be a bit more difficult than you’re used to with chlorine.
5. Chlorine Can Be Used as a Shock Treatment
As well as being a residual sanitizer, chlorine can be used as a shock treatment in order to eliminate a high level of contamination in the water.
Since chlorine is a strong oxidizer, a high concentration of this sanitizer will quickly oxidize organic substances, bacteria, viruses, and algae. This process also oxidizes and removes chloramines from the water.
Bromine doesn’t have the same oxidation properties as chlorine, and being a slower sanitizer makes it unsuitable as a form of shock treatment. As a result, it’s often paired with non-chlorine shock when shock treatment is needed.
Note: Non-chlorine shock is an oxidizer but not a sanitizer, and it’s not nearly as effective as chlorine shock.
6. Bromine Has a Less Potent Smell
This one is a bit confusing because bromine actually has a slightly more distinct smell than chlorine when it’s first added to your water, and it’s not necessarily a favorable smell either.
However, as mentioned earlier, chlorine produces chloramines when it reacts with contaminants, and enough chloramines will give off a very strong, unpleasant odor. This is what you might describe as a “strong chlorine smell“, which is really just used-up chlorine.
Bromamines (the byproduct of bromine) don’t give off the same nasty odor, so while the residual smell may be slightly less desirable than chlorine, it will never smell as bad as a chlorine pool under a heavy load.
7. Chlorine is More Widely Available
Chlorine is easier to find compared to bromine, which makes it a more convenient option when it comes to sanitizing your pool or hot tub.
As we touched on earlier, chlorine has a higher demand than bromine, which means it’s more heavily produced and therefore reaches more stores across the country. This is largely because chlorine is used outside of just pools and spas, such as in cleaning products and general water treatment.
While bromine is also used in general water treatment as well as flame retardants and pharmaceuticals, it’s not nearly as sought after.
8. Bromine is More Stable at High Temperatures
Bromine works better at higher temperatures, which makes it a good choice for heated pools and hot tubs.
This is because bromine has a higher molecular weight than chlorine which gives it a higher boiling point. As a result, bromine is less volatile and doesn’t evaporate as quickly at higher temperatures.
When talking about hot tubs in particular, the warmer temperature of the water can lead to a very high rate of chlorine loss, which means it needs to be checked and replenished more frequently.
When you consider that chlorine already lacks the staying power of bromine under normal conditions, the temperature issue just makes bromine all the more attractive.
9. Chlorine Can be Used in Liquid Form
Chlorine can be found in liquid form (typically 1-gallon jugs) which is very easy to add to your pool or hot tub water.
Liquid chlorine, or sodium hypochlorite, can be easily measured and poured directly into your water without having to pre-dissolve in a bucket. Because of this, unlike chlorine tablets or granules, it spreads very quickly in the water and begins working right away.
Bromine is only available in tablet or granular form. This is because liquid bromine is incredibly reactive and corrosive, which adds complexity issues to transportation and safety concerns around commercial use.
While there’s certainly nothing wrong with using tablets or granules, it does sometimes require additional steps and equipment such as a mixing container and floating dispenser.
Can You Use Both at the Same Time?
No, you shouldn’t use bromine and chlorine at the same time.
Remember when we said bromide forms bromamine when it reacts with contaminants in the water?
Well, some of your bromine also converts into bromide ions, which is a kind of inactive, “sleeping bromine”. These ions can also be added to your water through sodium bromide or algaecide products that contain it.
This is relevant because bromide ions are oxidized by chlorine, effectively “waking them up” and turning them back into bromine.
In other words, whenever you add chlorine to water that contains bromide ions (inactivated bromine), it eventually gets used up as it converts bromide ions back into regular bromine — and this reaction can make it difficult to maintain a consistent sanitizer level.
Important: Never place chlorine tablets and bromine tablets together in the same floater or feeder, as this can cause a dangerous chemical reaction.
Which is Best: Bromine or Chlorine?
Both bromine and chlorine will keep your swimming pool or hot tub water clean and clear, so there’s no wrong answer.
With that being said, bromine works better at higher temperatures and is softer on the skin, whereas chlorine is cheaper, works for longer, and doesn’t break down as quickly in UV (when paired with cyanuric acid).
Most people prefer the benefits of chlorine when it comes to maintaining a swimming pool, while many would agree that bromine makes more sense for a hot tub given its particular properties.
In the end, it really comes down to your pool or hot tub conditions as well as your own personal preference.