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Bromine has long been the preferred sanitizer for spas/ hot tubs due to it's unique properties. It has a slower dissipation at high temperatures than chlorine, is effective over a wider ph range than chlorine, has less odor and gas-off, and provides a certain degree of sanitation even when combined with organic contaminants. It is less reactive than chlorine, which means it is less irritating to skin and eyes, but works slower at the elimination of contaminants. These factors make it an excellent choice for spa sanitation, but it is important to understand how it works to be successful in its use.

Bromine use requires the establishment of a "reserve" or "bank" of inactive bromine, called bromide, from which active bromine is generated by means of oxidation or "shock". This reserve is established with the chemical sodium bromide, typically in a concentration of 10-15 ppm in the water. From this reserve bromine (hypobromous acid in solution) is formed by oxidation, typically with chlorine, monopersulfate (mps, non-chlorine shock), or ozone, though other oxidizers (such as hydrogen peroxide) will also cause this reaction. Recommended bromine residual is 3-5 ppm for a spa. It is important to note that sodium bromide cannot be tested with a bromine test kit or strips.

As bromine combines with organic contaminants, sanitizing the water, it is converted into bromamine, a harsh and irritating chemical. It is also important to note that a bromine test cannot differenciate between bromine and bromamines, so frequent oxidation is necessary regardless of residual test results to avoid irritation of skin and eyes.

Once a bromide reserve is established it cannot be removed by any reasonable means and the water must be drained to change sanitation methods. The addition of chlorine will just oxidize (shock) the bromamines and bromides into bromine without establishing a chlorine residual in the water.

Bromine tablets maintain the bromide reserve and oxidize the bromamine and bromide to generate bromine. Bromine tablets alone will not sanitize the water without a bromide reserve to work with. Bromine tablets are a combination of chlorine and a small amount of bromide to maintain the reserve. Bromide reserve decreases from dilution as water is added to make up for carry-out, or is dissipated slowly from uv (sunlight) and ozone exposure. Many bromine users do not use tablets and rely on manual addition of oxidizers for bromine generation, and sodium bromide for reserve maintenance. If using tablets, a weekly shock is recommended. If manually oxidizing only, treatment after each use is recommended at a minimum of once per week.

So, in summary, you first establish a bromide reserve of 10-15 ppm using sodium bromide, then oxidize with chlorine or mps to establish a bromine residual of 3-5 ppm (1-3 ppm with ozone), then shock frequently and maintain that residual with oxidation and, if you choose, tablets and/or ozone.

Here is an article from an industry publication if you want to study bromine maintenance further.




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  • 1 month later...

In actual practice, I haven't been able to achieve 1-3ppm sanitizer with ozone alone, as this requires a very powerful ozone generator / small spa.  Using my 2013 Grandee (500 gal), with corona discharge ozone generator, I have achieved just below 1ppm of bromine sanitizer under no load conditions.  This of course requires a very clean spa (recently purged with ahh-some) and  that no dust, critters, leaves or any contaminants are able to  enter the spa .  This last requirement is actually hard to achieve for outdoor portable spas,  but under these conditions I found that sanitizer level in my spa will  approach zero asymptotically (never get to zero but will  stabilize at some fraction of a ppm). 

the other consequence of bromine is that there is no such thing as a truly "non-bromine shock" because oxidizers (like chlorine or MPS) will convert sodium bromide to hypobromous acid.   This is not to contradict the recommendation to shock -- only to point out that doing so will raise the bromine sanitizer level!  For example, there is still  some merit in using MPS from time to time, because the conversion to bromine is not instantaneous,  and during this time the MPS will behave like MPS and oxidize contaminants directly. 

Unlike a chlorine spa, where one can use Hydrogen Peroxide to neutralize high levels of chlorine, no such neutralizing trick exists for the bromine spa

one of the key differences between the byproducts of oxidation for chlorine vs bromine is that, unlike chloramines,  bromamines are effective sanitizers and therefore not as problematic as are chloramines. 

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  • 5 months later...

In a Bromine system, 360 gallon spa:

What are the advantages of ph at 7.0-7.5 and TA balanced?

Clear water?

Impact on equipment?

I understand the aeration to inject air and lower the TA, but I get substantial foaming. so much that it spills over the sides of the spa in arm fulls.

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On 2/27/2021 at 7:43 AM, Pacopaco said:

What are the advantages of ph at 7.0-7.5 and TA balanced?

None, pH of 7.0 to 7.5 is actually too low for pH stability. Bromine is effective at a wide pH range and running your pH at 7.6 to 8.0 will minimize pH rise caused by outgassing of CO2 which is the main cause of pH rise in pools and spas. As far as TA balanced, what does that mean. Because of the aeration in spas and hot tubs a TA of 50 to 70 ppm is ususally best for pH stability because it also minimized the outgassing of CO2.


On 2/27/2021 at 7:43 AM, Pacopaco said:

I understand the aeration to inject air and lower the TA

aeration does not lower TA. Adding acid lowers TA, aeration raises pH without also raising TA by outgassing CO2.


On 2/27/2021 at 7:43 AM, Pacopaco said:

I get substantial foaming

This is not normal. Either your CH is too low, you have a lot of organics in the water (you need to shock), or there is detergent in the water (usually from swimsuits). these are the most common causes of excessive foaming. From your description I would suspect the detergent if you are getting that much foam when you open your air injectors. Please start a new thead in the hot tub water chemistry section about excessive foaming and post a full set of test results so we can help you solve the problem.

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