Bromine vs Chlorine for Hot Tubs

The quick answer: both keep a hot tub safe when kept in range.

• Bromine is the "steady" option. It holds up well in hot water and at higher pH, it's easy to run with a floater, and many people find it smells less. It costs more, and you can't switch away without draining.
• Chlorine is the "responsive" option. It's cheaper, faster-acting and easier to correct, but it needs dosing after soaks, and CYA builds up if you use dichlor only.

If you're new and want the simplest routine, either is fine. Choose based on the trade-offs below and stick with it.

How each works

Chlorine: you add dichlor granules or liquid chlorine/bleach. In water it forms hypochlorous acid, which kills germs and oxidizes contaminants. It's used up as it works, so you top it up, ideally after each soak, because that's when the contaminants arrive.

Bromine: you build a bromide bank by adding sodium bromide once per fill. An oxidizer then "activates" the bromide into bromine:

• shock: MPS (non-chlorine shock) or chlorine;
• or slow-dissolving bromine tablets (BCDMH) in a floater, which supply bromine continuously.

After bromine sanitizes, it returns to bromide, and the next shock reactivates it. That recycling is why bromine tubs feel low-maintenance.

Side-by-side

CDC figures are from its hot tub guidance; the 5 ppm chlorine soak limit is printed on many EPA-registered chlorine labels. Follow your tub's manual and your product labels too.

Bromine: the details that matter

• Start-up: add sodium bromide after each fill (about 30 ppm of bromide), then a small oxidizer dose sized to about 5 ppm bromine, not a full shock. Maintain bromine with a floater or granules. See how much bromine to add.
• Floater tablets (BCDMH) contain some chlorine too. They keep dissolving even when the tub isn't used, so adjust the floater's openings until the level holds steady.
• Shock weekly or after heavy use. MPS is popular because it reactivates bromide and lets you soak again soon (follow the label's wait time).
• Too much bromine is slow to fix. Leave the cover off and run the jets, or partially drain. Don't overfill the floater.
• Skin: many users find bromine water gentler with less smell, but bromine sensitivity exists. Some people get itchy or red skin from bromine specifically. If that happens, it may be the sanitizer, not the tub.

Chlorine: the details that matter

• The dichlor-then-bleach method is what many experienced owners use. After a fresh fill, use dichlor granules until CYA reaches about 30 ppm (dichlor adds about 0.9 ppm CYA for each 1 ppm chlorine). Then switch to liquid chlorine or plain bleach, which adds no CYA. That gives you a little sun and heat protection without CYA building up all fill long. CDC recommends not using stabilizer in hot tubs because it slows chlorine down, which is why this method keeps it low (about 30 to 40 ppm) and never lets free chlorine drop below 3 ppm.
• Bleach only, no stabilizer is the other option: no CYA at all, as CDC advises. Chlorine fades faster, so test before every soak.
• Dose after each soak. The amount depends on how many people soaked and for how long. The app suggests a starting dose from a conservative estimate; the test before your next soak shows whether it was enough.
• Chlorine falls quickly in hot, jetted water, so test before soaking.
• Avoid trichlor tablets in hot tubs. They're very acidic, add lots of CYA and can damage components. They're made for pools.
• The "chlorine smell" usually means combined chlorine (chloramines), not too much chlorine. Shock to clear it.

Which is better for an inflatable hot tub?

Inflatables (Lay-Z-Spa, Intex PureSpa, Coleman SaluSpa, MSpa and others) are small, run hot and are often used daily. Small volume means chemistry swings fast.

• Chlorine (dichlor-then-bleach) is the most common choice and matches most manufacturer starter kits.
• Bromine can work, but check your manual first. Some manufacturers specify which sanitizers and dispensers to use, and following the manual protects your warranty.

See our inflatable hot tub chemicals guide.

How to decide

Choose bromine if:

• you want a floater that keeps working between uses;
• your tub stays covered, so sun isn't a factor;
• you run warm water and pH that tends to drift up;
• you don't mind paying more for convenience.

Choose chlorine if:

• you're happy to test and dose after soaks;
• you want the lowest running cost;
• you like being able to correct things quickly;
• you might change sanitizers later.

Either way: test before every soak, keep pH and alkalinity in range, and drain on schedule. The sanitizer matters less than doing those three things.

Run either one with Spa Calc

Pick chlorine or bromine in Spa Calc:

• Chlorine: it walks you through dichlor-then-bleach and tracks CYA, or runs bleach only with no stabilizer.
• Bromine: it handles the bromide bank and the 2.25× test conversion.
• Both: every reading is checked against the soak range: soak, wait, or add this first.

One hot tub? Every feature, free. No account, no ads, and iCloud backup is included.

Safety

• Keep chemicals out of reach of children and pets, and keep them out of the water until it is back in range.
• Never mix chemicals. Never add acid and chlorine together: mixing them releases toxic chlorine gas.
• Add chemicals to water, never water to chemicals.
• Store chemicals sealed, cool and dry, apart from each other.
• Read and follow the product label. It always comes first.