Bromine or Chlorine in a Hot Tub: Which Should You Use?

Last updated: September 2026

There’s no better way to relax than in a hot tub in your backyard, summer or winter. But to keep the water healthy and clean you need to sanitise it, and that means picking between the two big names: chlorine and bromine.

Both do the job. Which suits you depends on your tub, how often you use it, how sensitive your skin and nose are, and how much effort you want to put in. In this article I’ll break down the pros and cons of each so you can make your own informed decision.

How chlorine works in your hot tub

Chlorine is the go-to sanitiser for pools, hot tubs and even drinking water. Once it’s in the water it kills bacteria and other contaminants on contact, and it also oxidises the waste that swimmers put in. It comes as granules, liquid and tablets, and they all do the same job.

In the UK, most chlorine granules are dichlor and most 20g tablets are trichlor, and both contain cyanuric acid (CYA), which builds up in the water. CYA slows down disinfection, and it only comes out when you drain water, so use it carefully. Unstabilised liquid chlorine (sodium hypochlorite) or calcium hypochlorite avoids the problem. My cyanuric acid guide explains why.

How bromine works in your hot tub

Bromine is the main alternative to chlorine, and it’s popular for hot tubs because it stays effective in warm water. Like chlorine it kills bacteria, but it behaves differently. It usually comes as slow-dissolving tablets, or as a two-part system where a bromide salt is activated by an oxidiser. You never handle it in its raw liquid form.

Bromine has a milder smell, and the sanitising by-products (bromamines) still kill bacteria. Chlorine’s equivalent, chloramines, are what cause that harsh “pool” smell and irritated eyes. Bromine doesn’t need cyanuric acid at all, and it is less affected by pH than chlorine.

Pros of bromine

• Much less chemical smell
• Generally gentler on eyes and skin
• Stays effective at hot tub temperatures
• Less affected by pH swings
• Safe for acrylic, vinyl, concrete and fibreglass tubs when used at the right levels
• Lasts longer between doses

Cons of bromine

• Usually more expensive than chlorine
• A weaker oxidiser, so you need to shock with a non-chlorine or chlorine shock to keep the water sparkling
• The tablets contain chlorine compounds, so it isn’t a fix for a true chlorine sensitivity
• Breaks down in sunlight, so it’s a poor choice for uncovered outdoor pools
• Needs a floating or cartridge feeder, which adds a little cost at the start

Chlorine vs bromine side by side

	Chlorine	Bromine
Target level	Free chlorine 3 to 5 ppm	Bromine 4 to 6 ppm
Speed	Fast acting	Slower, longer lasting
Dosing	Small, regular doses (after use, or every day or two)	Tablets in a feeder, topped up weekly or so
Smell	Stronger, especially if chloramines build up	Milder
Hot water	Used up faster as the water gets hotter	Stays effective at hot tub temperatures
Cost	Cheaper	Generally more expensive
CYA build-up	Yes, with dichlor and trichlor	No
Water clarity	Excellent oxidiser	Weaker oxidiser, shock regularly
Sunlight	Breaks down in sunlight unless stabilised	Breaks down fast in sunlight, so keep the cover on

How to apply them

Chlorine granules and liquid go straight into the water with the jets running. Tablets go in a floating dispenser. Never drop a tablet into the skimmer or leave it sitting on the shell. Bromine works best from a floating or cartridge feeder, and a single top-up can last a week or more. Whichever you choose, add chemicals with the pump running, never mix them and always follow the label. My chemical balancing guide covers the order to adjust things in.

Shocking

Both sanitisers need regular shocking to burn off built-up waste. With chlorine, shock with more chlorine (or a non-chlorine shock). With bromine, a non-chlorine shock also reactivates the bromide in the water, so it’s a good routine. See hot tub shock: what it is and how to do it.

Health considerations

• Many people find bromine gentler on skin and eyes, and much less smelly.
• If you have a real chlorine allergy, bromine tablets may not solve it, because they contain chlorine compounds. Talk to a doctor, and consider the non-chlorine options in alternatives to chlorine.
• Whatever you choose, keep the sanitiser in range. Low sanitiser causes more skin and eye problems than either chemical does at the right level.

Which should you choose?

• Choose chlorine if you want the cheapest, simplest option and you’re happy to dose a little and often.
• Choose bromine if the smell bothers you, you use the tub often and you like a set-and-forget feeder.
• Consider both if you struggle with cloudy water: many owners use bromine day to day and shock with an oxidiser.

Both are excellent options if you keep the water balanced and test regularly. For the day-to-day routine, read my beginner’s guide to hot tub maintenance. For the water-change side of things, see how to drain and clean a hot tub.

Need chemicals, filters or parts?

You’ll find spares, filters and water care products at parts4tubs.co.uk (UK) and parts4tubs.com (USA). If you’re planning your own build, have a look at my hot tub plans.

FAQs

Is bromine better than chlorine for a hot tub?

It’s better for some people. Bromine is gentler on the nose and stays effective at hot tub temperatures, but it’s usually more expensive. Chlorine is cheaper and a stronger oxidiser. Both work well if you keep the levels in range.

What levels should chlorine and bromine be in a hot tub?

Free chlorine 3 to 5 ppm, or bromine 4 to 6 ppm, with pH between 7.2 and 7.6 and total alkalinity between 80 and 120 ppm.

Can I switch from chlorine to bromine?

Yes. Drain and refill the tub and rinse the plumbing first if you can, then start on bromine. Don’t mix the two, and don’t use a chlorine feeder for bromine tablets.

Can I use bromine if I’m allergic to chlorine?

Not necessarily. Bromine tablets contain chlorine compounds. If you react to chlorine, check with a doctor and look at a non-chlorine system.

Why does my hot tub smell strongly of chlorine?

That smell is usually chloramines, which build up when there isn’t enough free chlorine to break down sweat and oils. Shock the tub, check your levels, and change the water if it keeps coming back.

Got a question about your own tub? Drop it in the comments below. I read them all.

Cheers,
Andi

You can also find me on my socials;

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi