A bottle of Bromine working as spa sanitiser

Bromine: guide to the no.1 spa sanitising chemical

The steaming heat of your hot tub is a harsh environment for sanitisers to work properly. So you need something tough; something with resilience that will nuke that unwanted algae and bacteria lurking in your spa pool. What you need is spa bromine

However, there’s a lot of misconception about spa bromine and how it can safely, and effectively, sanitise your hot tub. So let us take you on an informative bromine ride.

In this bromine guide, we’ll cover:

Let’s dive in.

What actually is bromine?

At room temperature, bromine is a red, fuming liquid, and that makes it unusual in the science world. This is because bromine is the only liquid element that’s not a metal.

This red liquid has quite a sharp, unpleasant stench, so bromine was named after bromos: Latin for “quite the stench” – or something like that. 

Bromine exists in nature as a compound (mostly as bromide salts). Bromide salts are extracted from places where they occur naturally, such as the Dead Sea

The extracted bromide-rich solution is then mixed with air and chlorine gas, which displaces the bromide via oxidation.

The reaction forms sodium chloride, and the oxidised bromide is released as a red gas that’s then collected, condensed, and purified. This collected gas is the chemically reactive bromine.

And if you’re even more interested in delving deeper into the science, you can read more about it here. However, chemically reactive bromine isn’t what you’re putting into your spa pool.  So how are my spa pool bromine tablets different?

How is spa pool bromine made?

Spa pool bromine tablets are actually bromo-chloro-dimethylhydantoin or BCDMH. This is a compound that contains active bromine bonded with chlorine and nitrogen.

This explains why those that have an allergy to chlorine cannot bathe in bromine sanitised water. When you put spa bromine tablets (BCDMH) into water, hypobromous acid (HOBr) begins to form from the bromine.

Hypochlorous acid (HOCI) will form from the chlorine, as long as the pH is between 6.5-9That shouldn’t be a problem considering the pH of your spa should be between 7.2-7.4.

HOBr has the antimicrobial properties your spa water needs to kill bacteria and other pathogens while HOCI has the oxidising properties. After HOBr has destroyed bacteria it turns into a bromide ion (a less reactive form of bromine holding onto an extra electron). Then, HOCI comes to the rescue and oxidises the bromide ion back into HOBr.

So good old chlorine actually helps bromine to do its job!

Who should use bromine to sanitise a spa?

Spa bromine is really versatile and can be used by most spa pool owners.

Do you find yourself in one of the following circumstances?

  1. You’re sanitising your spa for the first time.
  2. You’re sanitising your spa for the millionth time, but you need a refresher.
  3. Got an ozone unit and need to sanitise your spa.
  4. Decided to switch from chlorine to bromine to sanitise your spa pool.

If one of these sounds like you, then stick with us. 

We’ll cover the essentials first, and then give you the lowdown comparison between chlorine and spa bromine, before finishing up with some fascinating science around bromine as an element.

How to use spa pool bromine tablets to sanitise your spa pool

We’ll get right down to the nitty-gritty, in case you’ve got friends coming around, and you want to impress them with a sparkling spa pool.

Step 1: Get your equipment and supplies ready

You’re going to need the following:

Step 2: Check your water chemistry

You need to balance your spa chemistry before you sanitise with bromine. Make sure these are at the right levels:

  • pH: it must be between 7.2-7.4 for bromine tablets to do their job. 
  • Alkalinity.
  • Calcium hardness.

On this article you can learn more about spa chemicals and  how to balance your spa chemistry. You can also check out this helpful video about hot tub chemistry.

You may need to shock your spa pool before you add bromine. Shocking it will actually help the bromine to work more effectively.

Step 3: Make sure everything is running properly

Once you’ve got the chemistry sorted, you’ll need to check that your pool is at the right temperature, and the filtration system is running. 

All checked and ready? Great – now we get to the good stuff!

Step 4: Add spa bromine tablets to your spa pool

It’s always best to read the manufacturer’s instructions, which you should do next. We’re dealing with tablets here, not liquids or granules.  So, as a general rule of thumb, start with one spa bromine tablet for every 600 litres of spa water.

Remember how we mentioned that you may be looking to use spa bromine under different circumstances?  Here’s where you can skip to the section that best applies to you.

Starting from scratch: spa pool start-up with bromine

You’re the owner of a brand-new spa pool? Congratulations! When you first fill your spa with fresh water you’ll need to:

  • Aim for a bromine reading of 3-5ppm (parts per million).
  • Maintain this for one hour.
  • Then add additional bromine tablets as needed.

Fill your tablet feeder to capacity or turn your inline feeder up to max on the control valve to reach this reading.

How to add spa bromine tablets to a floating tablet feeder

  1. Carefully add bromine tablets to your tablet feeder and secure the feeder lid.
  2. Place the feeder into your spa and hold it under the water for a few seconds.
  3. Let the feeder bob around in your spa whenever it’s not in use.

If you have an ozone unit, a floating tablet feeder is the easiest way to keep spa bromine levels topped up. 

You’ll just need one or two tablets dissolving in your feeder rather than a few.

How to add spa bromine tablets to an inline tab feeder

  1. Turn your filtration system off.
  2. Turn the feeder control valve off and wait one minute to allow any gas to disperse.
  3. Twist the feeder cap openkeep your face away and do not inhale the fumes.
  4. Carefully place bromine tablets into the feeder and screw the feeder cap back on.
  5. Reset the feeder control valve to your regular setting or start at 50%.
  6. Test the bromine levels every half an hour or so until it’s reduced to 3-5ppm.

Now your spa is ready. You can hop in for a much-deserved soak!

Switching from chlorine to bromine sanitiser

If your spa has an ozone unit, you still need to top up sanitiser levels with bromine tablets; you’ll just be using a lot less. It’s easier if your spa is currently sanitised with chlorine as all you’ll need to do is stop using chlorine and start using bromine.

Unless chlorine is distributed by a tablet feeder or salt chlorinator. When residues of chlorine and bromine come into contact with each other, the results can be dangerous.

If you’re in this situation, you’ll need to:

  1. Replace your tablet feeder.
  2. Discontinue using a salt chlorinator.
  3. Then, drain your spa and flush the lines.

It’s worth noting that once you start using bromine, it can be difficult to go back.

What about switching back to chlorine, after using bromine?

If, down the track, you decide to switch from spa bromine to chlorine sanitiser, the process can be tricky. 

Adding chlorine to a bromine sanitised spa will only make the bromine stronger, so you’ll need to drain and refill your spa instead.

Maintaining the sanitising effect of spa bromine

Depending on how frequently your spa pool is used, test for total bromine levels every one to three days.

Then you’ll only need to top up spa bromine tablets during times when a total bromine reading is lower than 3ppm or when a bromine tablet has dissolved completely.

Because it’s now just a case of maintaining regular spa bromine readings at 3-5ppm. As easy as all of this may seem, bromine isn’t foolproof all of the time.

If your bromine readings are lower than 3ppm or higher than 5ppm, we’ll guide you through what to do next.

What to do if bromine levels are wrong

As with all spa pool chemistry, you need to keep an eye on the levels of bromine and adjust them if they’re too low or too high. Let’s see what to do in each case. 

What to do if the total bromine reading is too low

When your spa has low total bromine you’re risking a build-up of organic matter that’ll turn your spa into a cloudy, friend-fleeing cesspool. 

Start with these steps:

  1. Check that your testing strips haven’t dampened or expired.
  2. Test for balanced pH, alkalinity and calcium hardness.
  3. Check for any visible signs of algae.

If all is well so far, then you can increase the amount of spa bromine in your spa:

For inline tablet feeders:

  • Increase the feeder control valve to one notch per day.
  • Take a reading after 24 hours.
  • Repeat this process until bromine reaches 3-5ppm.

For floating tablet feeders:

  • Add one extra tablet into the feeder.
  • Take a reading after 24 hours.
  • Repeat this process until bromine reaches 3-5ppm.

See? Low total bromine levels can be fixed by carefully adding more bromine!

What to do if the total bromine reading is too high

High total bromine readings are tricky, because once the chemicals are in your spa, you can’t just fish them out. If this happens, don’t go soaking in the spa, because you may experience these side effects:

  • Watery or stinging eyes.
  • Skin rashes or burning.
  • Respiratory problems. Please seek medical advice if this happens!

So here’s what you can do when bromine levels are too high in your spa, if you have time:

  1. Take your spa cover off.
  2. Wait a day or two.
  3. Test until total bromine reaches 3-5ppm.

If instead you’re in a rush:

  1. Remove half of the water in your spa.
  2. Refill with fresh water.
  3. Run the filtration system for half an hour.
  4. Balance the spa chemistry.
  5. Test until total bromine reaches 3-5ppm.

You can either wait for the sanitiser to break down over time or dilute the sanitiser with fresh water. So now you know how to use spa bromine tablets. 

But perhaps you’re still unsure about whether to swap your chlorine for bromine, or which product is best for you. We’ll do a quick comparison by looking at the pros and cons of each product.

What’s the difference? Spa bromine vs. chlorine

Chlorine paves the way for bromine to work (more about this in the next section), but any doubts you have about bromine may change after learning about the differences between the two.

Ding, ding, ding. 

The battle of the sanitisers has begun: Spa bromine vs chlorine.

Pros and cons of chlorine

Pros of chlorine:

  • Dissolves quickly. 
  • Initially cheaper to buy.
  • Kills organic matter such as algae quite quickly.
  • More than one dispensing method.
  • Breaks down more slowly in UV light (the sun).

Cons of chlorine:

  • Chlorine breaks down and produces chloramines. They cannot be re-used for sanitising, so you have to keep adding chlorine to get rid of them.
  • Tends to have more of an odour.
  • More stable in temperatures below 18°C (not great for hot spa water).
  • Worse for those with skin sensitivities.
  • Has a more extreme pH.

Pros and cons of spa bromine

Pros of bromine:

  • Bromine molecules can be reactivated (so you need to use less bromine).
  • Tends to have less of an odour. 
  • More stable in temperatures above 23°C (great for hot spa water).
  • Better for those that have skin sensitivities.
  • Has a pH closer to what you’re maintaining in the spa.

Cons of bromine:

  • Slow dissolving time.
  • Initially more expensive to buy.
  • Takes longer to kill organic matter such as algae.
  • Only comes as a tablet.
  • Breaks down quickly under UV light (the sun).

When you’ve got a few people soaking up the fun in your hot tub, the pH levels can change drastically compared to a spacious pool. This is when bromine proves its mettle. Chlorine isn’t effective in a pH above 8.0, whereas spa bromine is, and it works better in heated water. 

The initial cost of spa bromine is generally a bit higher than chlorine’s price tag. That doesn’t mean you can’t use chlorine in your spa; you’ll just be constantly adding more and more chlorine as it’s killed off by the heat. And you’ll still need to shock your spa pool, whether you choose bromine or chlorine. 

If you’re biting away at your nails, torn between the two, why not have both? Because you can.

Use spa bromine as a sanitiser, due to its suitability in warmer water, and use dichlor (chlorinated shock) or lithium-based chlorine as a spa shock treatment, due it being a powerful oxidising agent.

If you’re team bromine all the way, you can use spa bromine as a sanitiser and use a non-chlorinated shock treatment instead. Check this for more information on the differences between chlorine and bromine

Still curious? We’ve got more in store for you, if you’re keen on knowing more about the science behind bromine. Keep reading and also check our spa sanitiser guide.

Can I get sick from the bromides in my spa?

Bromine aside, what about the safety of bromide – that chemical produced from bromine that is hanging about in your spa?

Well, we’ll start by mentioning that the safe daily intake of bromide ion in humans is limited to 1mg per kg of body weigh. 

Which is a relatively conservative recommendation considering the result of this WHO study, where there were no negative health effects in humans who were dosed with 9mg of bromide ion per kilogram of body weight.

But the amount of total bromine required to effectively attack bacteria in your spa is 3-5ppm, and 5ppm equates to 5mg per litre of water. Therefore if a person weighing 60kg was to exceed the recommended daily intake of bromide ion at 1mg/kg, they would need to consume at least 12 litres of spa water

That’s right – they’d need to hop in and thirstily drink 12 litres of your dazzling spa water. They’d probably rather refresh themselves with a cold beer from your fridge. 

As long as sanitisers are used with caution, the dangers don’t necessarily come from the chemicals, but what can happen when you don’t use a sanitiser. 

Spa bathers can get ill from ingesting microbes in dirty spa water. You should protect them by safely sanitising your spa.

So is spa bromine safe?

Remember how we mentioned that there are some misconceptions about spa bromine’s safety? 

Well, when spa pool bromine tablets have dissolved in your spa water and after that lengthy chemical reaction, no bromine remains in your spa water.

So – it’s not dangerous!

Just as long as you balance your spa’s pH range between 7.2-7.4 prior to using spa bromine tablets, and test for total bromine (hypobromous and hypochlorous acid) after 20-30 minutes.

Where can I find spa bromine tablets?

Spa pool bromine tablets can be found at speciality spa supply stores. You might also want to check  the bromine dispenser.

But it doesn’t end there. You’ll need a few more supplies than that to keep your tub happy. 

Happy soaking!

About the author
Adrian Hill
Adrian Hill

Hey! I'm Adrian, founder and pool expert here at Dolphin Pacific. I love spending time with family, fishing, and have been known to brew my own beer.

Signup To Our Newsletter!
Step by Step guide to pool cleaning Graphic square
Download The Guide

Learn how to keep your pool sparkling clean step-by-step!

How our ordering process works.

Once you have added the products to your cart, initiated checkout and completed the order, it is sent to our sales team. We will place the order with our stockists and you will be contacted when your order is ready to be picked up locally, or delivered to your door.

When do I pay for the products?

Payment is made to our stockists. If you choose to pick up your order from the stockist, payment will be required upon receiving the order. For deliveries, you will enter your card details through a secure form and the order will be sent to your door.