Pool-chemical safety: Never mix bromine and chlorine products. Pentair’s Rainbow 320 feeder guide says “UNDER NO CIRCUMSTANCES MIX Trichlor or Bromine with Calcium Hypochlorite, with other forms of concentrated chlorine or with other chemicals,” warning that “FIRE AND/OR EXPLOSION MAY RESULT.” CDC’s chemical-use poster says never to mix different pool chemicals and never to add water to a pool chemical.

For an outdoor pool, chlorine is the usual choice: stabilizer (CYA) protects it from sunlight, and it works with salt chlorine generators. Bromine makes more sense indoors and in hot tubs, where sunlight isn’t an issue and higher pH is common. The MAHC annex says bromine “is destroyed rapidly in sunlight” like chlorine, and that CYA “does not provide a stabilizing effect for bromine.”

Side by side

All figures come from CDC’s 2024 Model Aquatic Health Code (MAHC) and its annex unless noted.

Chlorine Bromine
MAHC minimum, pools 1.0 ppm free chlorine; 2.0 ppm with CYA 3.0 ppm
MAHC minimum, spas 3.0 ppm 4.0 ppm
MAHC maximum Set by the product label 8.0 ppm while swimmers are present
Active form at pH 7.5 49% HOCl (no CYA) 94% HOBr
Active form at pH 8.0 23% HOCl 83% HOBr
Stabilizer (CYA) Developed to protect chlorine in pools “Does not provide a stabilizing effect”
What a home test reads Free chlorine Total bromine only
Salt chlorine generators Designed to make it Hayward and Pentair advise against bromine

Sunlight and stabilizer

This is the biggest practical difference for a backyard pool. The MAHC annex says bromine “is also not very common in outdoor POOLS because like CHLORINE, bromine is destroyed rapidly in sunlight.” It adds that CYA “was developed to combat the problem in chlorinated POOLS but does not provide a stabilizing effect for bromine.”

Chlorine’s trade-off is that the same CYA slows it down. CDC raises its minimum free chlorine from 1 ppm to 2 ppm when you use stabilizer. The stabilizer guide covers the ranges.

pH and odor

Bromine holds up better as pH rises. The MAHC annex says “at pH of 7.5, 94% of bromine is HOBr, whereas at the same pH with no CYA, HOCl is 49% in chlorinated water. At pH of 8.0 bromine still has 83% HOBr, while in a chlorinated water, HOCl is 23%.”

The annex gives two reasons bromine is common in indoor commercial spas. First, “bromamines (bromine and ammonia combined) do not produce irritating odors as do chloramines.” Second, “bromine efficacy is less impacted than CHLORINE’s at a higher pH, which typically occurs in a SPA environment.”

pH still matters for the water itself. See the pH and alkalinity guide for target ranges.

Levels and testing

Bromine is held at higher numbers than chlorine. The MAHC requires at least 3.0 ppm bromine in public pools and 4.00 ppm in spas, and no more than 8.0 ppm while the pool is open. The annex notes that “every jurisdiction that allows bromine as a DISINFECTANT requires bromine at higher concentrations than CHLORINE,” and that CDC recommends 4–6 ppm for bromine.

Product labels set the working range. The annex says registered bromine products carry “use concentrations ranging from 1-8 ppm (mg/L), depending on the product,” so follow the label on your container.

Testing works differently, too. The MAHC says commercially available kits “are not capable of distinguishing free bromine” from combined bromine, so the result is total bromine. The annex explains that kit makers take a chlorine value and multiply it by 2.25 to report bromine. Use a kit or strip that is labeled for bromine.

The product forms

The MAHC lists two compounds used to add bromine: DBDMH (1,3-dibromo-5,5-dimethylhydantoin) and BCDMH (1-bromo-3-chloro-5,5-dimethylhydantoin). It also requires that only EPA-registered bromine and chlorine products be used.

As an example, In The Swim 1 Inch Bromine Tablets Plus (25 lb) is listed by In The Swim at “98% active ingredient,” with “61% available bromine” and “27%” available chlorine. In The Swim says the tablets dissolve “much slower than chlorine,” must not be mixed with chlorine in an automatic feeder, and “cannot be dispensed in a used chlorine feeder.” It also says the bromides left in the water can be reactivated by superchlorinating. That is In The Swim’s claim, so check the container label for your product’s directions.

For chlorine tablets, see the 3-inch chlorine tablet comparison .

Salt systems and feeders

If you have a salt chlorine generator, the makers’ manuals settle the question:

  • Hayward’s AquaRite manual: “Hayward does not recommend using the AquaRite to generate bromine.”
  • Pentair’s IntelliChlor manual: “Do not use this device in conjunction with bromide products.” It also rules out sodium bromide as a salt source.

For tablet feeders, read the feeder’s own guide. Pentair’s Rainbow 320 guide says bromine tablets or sticks may be substituted for trichlor in that feeder, adding “DO NOT MIX.” It notes that using bromine tablets in that feeder “is not NSF certified.” If you aren’t the original owner or aren’t sure what chemical was used, it says to “be SAFE and flush thoroughly with fresh water,” and to take care when removing the cap and not inhale the fumes. The Rainbow 320 review covers that feeder.

When bromine makes sense

Bromine fits best where the MAHC annex says it is common: indoor spas and hot tubs, where sunlight isn’t a problem and pH tends to run high. Chlorine fits best in outdoor pools, which can use CYA, and in any pool with a salt chlorine generator, since Hayward and Pentair advise against bromine with their systems.

Whichever you choose, keep the two chemistries apart: separate containers, separate scoops, and a clean, flushed feeder before you switch.

Sources

Facts were checked against these sources on October 9, 2026. This is researched buyer analysis without hands-on testing.

FAQ

Is bromine better than chlorine for an outdoor pool?

Usually not. The MAHC annex says bromine is not very common in outdoor pools because, like chlorine, it is destroyed rapidly in sunlight, and cyanuric acid (stabilizer) does not stabilize it the way it does chlorine.

What bromine level does a pool need?

The MAHC requires at least 3.0 ppm bromine in public pools and 4.0 ppm in spas, with a maximum of 8.0 ppm while swimmers are present. The annex notes CDC recommends 4 to 6 ppm, and that registered products range from 1 to 8 ppm depending on the product, so follow your product’s label.

Why is bromine used in hot tubs?

The MAHC annex gives two likely reasons for its use in indoor commercial spas. Bromamines don’t produce the irritating odors chloramines do, and bromine loses less effectiveness than chlorine at the higher pH common in spas.

Can I use bromine with a salt chlorine generator?

Hayward says it does not recommend using the AquaRite to generate bromine, and Pentair’s IntelliChlor manual says not to use the device with bromide products. Check your own system’s manual.

Can I put bromine tablets in my chlorine feeder?

Never mix them. Pentair’s Rainbow 320 guide allows bromine tablets in place of trichlor but says “DO NOT MIX” and to flush the feeder if you are unsure what was used. In The Swim says its bromine tablets cannot go in a used chlorine feeder.