Chlorine vs. Bromine: What’s the Difference?

chlorine and bromine tabletsIn today’s post I’ll be discussing some of the differences between chlorine and bromine sanitizers. Many people assume chlorine is for pools and bromine is for spas, but that doesn’t have to be the case.

Chlorine is by far the most popular choice for sanitizing swimming pools. It is less expensive than bromine and is available in many forms: 1” tablets, 3” tablets, sticks, granular and liquid.  The 3” tablets are the most popular for general pool chlorination. If you would like more information about the various types of chlorine, check out Brett’s postWhat Pool Chlorine Type is Best for your Pool?”.

The Difference between Bromine and Chlorine

chlorineChlorine dissolves fairly quickly to begin sanitizing the water. Chlorine tablets or sticks can be used in floating dispensers, in line or offline chlorine feeders, or placed directly in the skimmer basket, though this is not recommended. Granular chlorine can be pre-dissolved in a bucket of water and poured around the pool.

As chlorine begins disinfecting the water or killing algae it forms compounds called chloramines. This is a chlorine molecule combining with Ammonia or Nitrogen. These compounds produce the chlorine smell that many people are associate with swimming pools. As these compounds continue to build up over time they reduce the killing power of the chlorine, and a shock treatment is needed to burn off these inactive chloramines – so that fresh chlorine (or “free” chlorine) can continue to disinfect the pool.

Reaching “breakpoint” chlorination is an important threshold, where everything in the pool is oxidized, and the strong chloramine bond can be broken. Imagine a “shock” or a lightning bolt, ripping through the water, killing anything organic, and removing improper molecular combinations. For more information on shocking the pool, see Lauren’s post on “The Many Types of Pool Shock“.

Chlorine is easily broken down by sunlight and so it is highly recommended that you use a stabilizer, also called conditioner – to prevent this premature breakdown, if your pool is located in the outdoors.

Bromine is only available in 1” tablets and it must be used in a feeder, it may not be used in a floating dispenser or placed in your skimmer basket because it takes a very long time to dissolve. Bromine tablets will only dissolve as water rushes over them through a bromine feeder.

Due to its slow-dissolving nature, bromine can take longer to build up a residual in the water and is therefore more difficult to raise quickly if the bromine level drops.

Bromine produces compounds called bromamines as it works to disinfect the water, but unlike chloramines, they still remain active and continue to disinfect and don’t produce odor, or burn the eyes. Bromamines can also be reactivated by a shocking treatment and be returned to their full strength, while chloramines are simply burned off and removed from the water.

Those with very sensitive skin may prefer bromine because it generally does not cause as much skin and eye irritation as chlorine sometimes can (though this really shouldn’t be much of an issue if you keep your pool properly balanced).

Bromine is far more stable and effective in high temperatures, which is why it is almost always used in spas and hot tubs. The money you will save by purchasing chlorine over bromine for use in a spa is usually negated rather quickly due to the fact that you will need to use much more chlorine to keep the spa sanitized. Bromine tablets can be used in small floating feeders in spas or hot tubs because they hold such a small amount of water and the bromine can disperse more effectively.

Bromine is also more effective over a wider pH range than chlorine. This is important in the spa environment, where 4 people jumping in suddenly can cause extreme swings in the spa pH level. At pH levels above 8.0, chlorine becomes sluggish and it’s efficacy drops below 50%. Not so with bromine, however, which retains efficacy through higher pH ranges.

Which is better for me, Bromine or Chlorine?

So, Chlorine or Bromine? Chlorine and bromine are both very effective sanitizers, but some people may have more specific requirements or preferences that may make them choose one over the other. If you are a pool owner that routinely forgets to add sanitizer and test your water, then chlorine may be the best choice because it is easier to quickly raise or lower the chlorine levels in your pool. Those with very sensitive skin may prefer bromine. If you do decide to make a switch from chlorine to bromine and you are currently using an automatic feeder, you will need to purchase a new feeder because mixing chlorine and bromine can cause a dangerous chemical reaction.

If you have any questions about which pool sanitizers are right for you, please give us a call, we’re always here to help you make easier decisions regarding your pool!





Jackie Wolski
InTheSwim Staff Blogger


Chlorine vs. Bromine: What’s the Difference? — 14 Comments

  1. Hi, I am changing my chlorine for bromine in my spaberry (125 gallons/470 liters.) Can I use the same test strips to test the bromine levels as I used to test the chlorine? After two days of bromine (dispenser closed down tight) the reading is in the purple or very high. I have removed the bromine tablets and allowed just one in the dispenser (still closed down tight). i will check again in a day. Are there special bromine test strips that measure BR, PH and Alkalinity?

    • Hi Rich, good question. Bromine is 2.5x heavier than chlorine, so when testing with a chlorine test kit, multiply the result by 2.5 to establish the equivalent bromine reading. There are Bromine test strips however, AquaChek “Red” is bromine (yellow is chlorine). Another thing about bromine, is that tablets work best when the spa has a ‘bank of bromide ions’ built up already. Many spa owners add a small amount of Bromide Ions ‘Brom Booster‘ to the spa after draining and refilling, to establish an initial level of bromide (which converts to bromine with a shock oxidizer), instead of waiting 2-4 weeks for it to build naturally, from bromine tablets.

    • Hi Roland, I would think the opposite, but it’s not usually bromine or chlorine that causes heat exchangers to break down. Salt pools with a copper heat exchanger can experience corrosion and galvanic problems and damage to gas pool heater cores or exchangers, and many salt pools opt for cupro-nickel heat exchangers for this reason. For non-salt pools, it’s generally a consistently low pH and alkalinity, combined with other water balance problems, that can strip out the copper, and wear thin the copper tubes, leading to pinhole leaks and failure. Very high lime and calcium content can clog heater tubes in some cases. But chlorine or bromine, kept at normal levels, pose no harm to copper heat exchangers.

  2. Hi. I’m 63 years old. I’ve been a swimming pool swimmer my whole life. Never had a problem. All of a sudden in the past 3 years, whenever I go swimming in my pool, I get a rash all over my body. It’s terrible. It takes a few days then it goes away. IF I go in again, same thing happens. I havn’t gone in my pool in 2 years.I’m thinking I can’t take Chlorine any more. Any advice? Thanks.

    • Hi Debbie, I haven’t heard of chlorine giving people rashes, but if a pool had high levels of certain bacteria like pseudomonas, that will cause a rash. Or it could be from using someone elses towel or laying on an infected lounge chair. At my pool this summer, a bunch of divers all caught a red bumpy skin rash, and they all blamed the pool – turned out to be a ‘divers shami’ towel that they were sharing…

  3. Question,

    I have a galvanized stock tank that we’ve made a soaking tube out of (Thank you Pintrest!!). It’s 5′ round, would bromine or chlorine be better? How much should I use and how often? Pam

    • Hi Pam, I’ve heard of those pools, very popular now. I would use a chlorine floater, with 1-2 tablets at a time, or however many it takes to produce a constant and consistent chlorine level of 1-2 ppm, as tested by your test kit. Also immportant is to keep your pH level in the 7.2-7.6 range, using pH adjusters as needed (up or down) to keep pH within range. You can shock the pool periodically with 1/2 lb of Dichlor shock (Di-Zap is our brand). Bromine can also be used, but since the tub is outdoors, and if it gets sun, stabilized tablets and shock may be a better choice.

    • It may be, bromine is known to be ‘softer’ than chlorine, in regards to skin irritation. Psoriasis affects people differently from what i understand – chlorine or bromine may irritate psoriasis symptoms on some people, and not so much with others. I am not aware of any ‘skin studies’ however that could prove the point, but the general thought is that bromine is a bit gentler on skin, as compared to chlorine. (all else being equal)

  4. if I switch to bromine do I have to empty my hot tub and start with new water? you said I would need a new feeder due to chemical reaction caused by mixing both and this suggested to me I need to change water also that contains chlorine

    • Hi Evelyn, no need to drain if going from Chlorine to Bromine, but if going from Bromine to Chlorine, the pool (or spa) should be drained, to remove the bromide ions, which will continue to produce bromine. And as you mention, chlorine and bromine should never contact each other. If you were using a bromine feeder or floater, it should not be used for chlorine tablets (and vice-versa), as the residues in the feeder can react with the similar but very different chemical.

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