The most popular spa sanitizers available are chlorine and bromine, which are both halogens. Halogens are highly reactive elements, a characteristic that makes them ideal for sanitizing and oxidizing contaminants in water. Both are available in convenient forms for use in your spa or hot tub. But there are a number of factors to be considered. If your spa is connected to your pool or has a spillover, the pool and spa will share the same sanitization system. For free-standing “portable” swim spas or hot tubs, how do you choose which product is best to use?
The best place to start is by first consulting with your spa dealer and reviewing the manufacturer’s owner’s manual for recommendations. Proper treatment of spa water is easiest when a program is followed to ensure that products used for sanitization, oxidation, and water balance all work well together. Plus, many spas and hot tubs feature pre-installed supplemental sanitizer systems with ozone, minerals, ultraviolet C (UV-C) or Advanced Oxidation Process (AOP) systems that should be taken into consideration as well.
Both chlorine and bromine are available in a variety of convenient forms with a wide array of brands and products on the market. But no matter which sanitization method you choose for your spa or hot tub, regular water testing should always be your guide to on-going water care and treatment.
When selecting a sanitizer for your spa, it is important to note that you must select only one — chlorine or bromine — so it's worth doing your research before deciding between the two. Because while it is possible to change your selected sanitizer program, you would need to fully drain the spa, flush water lines, and rinse components first before switching.
Chlorine vs. Bromine: Cost & Convenience
Both chlorine and bromine are available in a variety of convenient forms including the popular granules and tabs (1 inch tabs are recommended for spas). When it comes to cost, chlorine sanitization products are typically less expensive than bromine. With regular, ongoing use, costs could add up. However, keep in mind that the cost difference between the two choices may not be a big issue for spas since they typically require much less sanitizer than pools because of their smaller size and pre-installed supplemental systems. If you're a pool owner, you are likely already accustomed to using chlorine sanitizers and there may be cost savings in using the same sanitizer in your spa as well. But be sure to check with your dealer or manufacturer to confirm the differences in form, size, and/or concentration of chlorine required for spas vs. pools.
Chlorine vs. Bromine: Spa User Experience
Bromine is more commonly used in spas because it offers superior performance at increased bather loads and higher pH. When contaminant levels are high, as they are with high-use, high-temperature spa applications, disinfection byproducts are frequently formed.
The byproducts formed by bromine are known as bromamines. Bromamines are mild in odor and are usually less irritating to the eyes and to mucous membranes than their chlorine counterpart. However, you'll need to regularly shock your spa, with a strong oxidizer such as chlorine or monopersulfate (MPS), to regenerate the bromamines back to their full-strength.
On the other hand, when chlorine reacts with bodily fluids or other contaminants it forms chloramines, also referred to as "combined chlorine", which can produce strong, unpleasant odors and can cause skin irritation from the conditions of a poorly maintained pool or spa. Supplemental treatment systems that are installed on spas can help to eliminate or reduce the formation of combined chlorine. Once combined chlorine levels reach 0.5ppm, it is recommended to remove the combined chlorine by shocking your pool or spa to 10 times the combined chlorine level.
To help stabilize your chlorine levels, cyanuric acid can be used to protect chlorine from sunlight. If your spa or hot tub is receiving a lot of sunlight, adding cyanuric acid will help prolong the life of the chlorine by 3-10 times. Note that cyanuric acid does not work for bromine sanitizer.
Chlorine vs. Bromine: Testing
Free and combined chlorine levels can be monitored using DPD and FAS-DPD test methods and some test strips. OT should never be used to test a spa that is sanitized by chlorine because it cannot distinguish between free and combined chlorine. Detection is key because chloramines can be noticeable to bathers at levels as low as 0.2ppm, and should be eliminated completely, via shocking, if levels reach 0.5 ppm.
The FAS-DPD titration is an excellent choice for measuring free and combined chlorine. It’s recommended for spa owners to use a combination kit that includes FAS-DPD, such as the K-2006. And, for those that prefer the convenience of test strips for routine testing, the K-1515-A is a great supplemental kit to make sure combined chlorine levels are kept fully under control.
Total bromine can be monitored with OT, DPD, and FAS-DPD test methods, and some test strips. Because bromamines do not have the objectionable properties of chloramines, bromine sanitizer tests can be simpler because they do not need to differentiate between the free and combined forms like chlorine testing does.
Note that in water testing, the primary difference between chlorine and bromine is that bromine weighs much more than chlorine — 2.25 times more. If you ever need to convert “chlorine ppm” into “bromine ppm” for testing, you should adjust for the weight difference by multiplying by 2.25. (For simplification, 2.25 is sometimes rounded to the value of 2.)
Whether you choose chlorine or bromine, check your spa manufacturer’s recommendations for proper sanitizer levels. All Taylor residential liquid test kits include testing for total bromine and either free or total chlorine, making them convenient for homeowners who use chlorine to sanitize their pool and bromine for sanitizing their spa.