Bromine Hot Tub – getting the chemicals right

When I first got a Bromine Hot Tub (that is a hot tub using bromine as the main chemical instead of the more common chlorine), it was a complete disaster. I wasn’t given very good information, either by the people who installed it or in the documentation they left behind. It took me quite a bit of time and research to figure out how to handle it, and I’m glad to say everything is well under control now. In this article, I’ll walk you through what you need to do – it’s not very hard.

Why Bromine?

Why did I choose bromine and not chlorine? There were two reasons really, based on what I’d read. First, bromine is meant to be a softer chemical than chlorine and hopefully not as damaging to the skin. It certainly doesn’t smell as much as chlorine. Second, bromine is supposed to work better than chlorine at the higher temperatures of a hot tub.

Bromine is a softer option than chlorine and would be recommended if you or a family member/friend have sensitive skin as chlorine can be harsher on the skin and eyes.

Bromine tablets also have less of an odour as the strong scent of Chlorine although chlorine scents only become strong in the dirty water.

From https://www.hottubsuppliers.com/bromine-or-chlorine

Get a good testing kit

In my earlier post – Pooltester kit – avoiding Bromine Hot Tub nightmares – I explained the need to get a proper pool testing kit. This is a must. Don’t rely on those flimsy testing strips as they tend to give misleading readings. Using these would be like trying to drive a car with your eyes closed – you can do it, but you’re sure to crash sooner or later. Get a good testing kit!

The necessary chemicals

These are the things I’d recommend stocking up on;

1. Bromine Tablets
   • The key ingredient to keep the bromine level correct to keep the water clear. They are not important at the initialisation stage, but they are key for ongoing water cleanliness.
   • This is not a recommendation, just that the ones I use are Fi-Clor Spa Bromine Tablets.
2. Sodium Bicarbonate
   • Just simple sodium bicarbonate, or bicarbonate of soda, that you use in the kitchen. This chemical raises pH and alkalinity. No need to buy fancy versions in pool chemical shops that might be called something like “pH up”, it’s just sodium bicarbonate. I buy this in bulk (like 10 kg at a time) and it’s cheap.
3. Dry Acid
   • This is needed to reduce the pH or alkalinity of the spa. I haven’t yet been able to find a simple, generic version of dry acid and I’m currently using Fi-Clor Spa pH & Alkalinity Reducer.
4. Borax
   • This is standard “Borax” (Borax Decahydrate) that’s actually not that easy to buy in the UK. It’s needed to raise the pH but without raising the alkalinity at the same time (sodium bicarbonate also raises pH, but it raises alkalinity too). I most recently purchased Borax from HD Chemicals in the UK.
5. Sodium Bromide
   • this is the essential chemical that’s only needed at the initialisation phase when you fill the tub with fresh water. You don’t need very much of this. I bought 500 grams of ‘Sodium Bromide Pharmaceutical Grade’ almost 3 years and I still have some left.
6. Bleach
   • Common laundry bleach is really just chlorine, and it’s the cheapest way to access chlorine. Just get basic, unscented bleach from the laundry aisle at you supermarket. Pure bleach, nothing else. Ideally, 5-6% concentration. Why do we want chlorine when this is meant to be a bromine hot tub? Well, a small amount of chlorine is needed to activate everything – even the bromine tablets have a small amount of chlorine in them.

Initialising your hot tub

1. Fill your hot tub with water
   • fill it up to the level described in your instructions
2. Keep the heating off (or very low) until you have the chemicals under control
3. Get the Alkalinity close to a reading of 100, at least between 80 and 120
   • test the water, using you testing kit, and check its alkalinity – no need to worry about anything else at this stage
   • if it’s above 120, turn on the pumps to get the circulation going and add some dry acid. You’ll just have to get used to how much acid makes a certain amount of difference in your spa. Use the same size measuring cup every time so you’ll get to know how much you need to make the difference required.
   • if it’s below 80, start the circulation and add some Sodium Bicarbonate
   • 30 minutes after adding a chemical, check the alkalinity again
   • keep doing this until the alkalinity is within the range of 80-120
   • a good tip here is try to get the alkalinity very close to 100 – it makes everything else a bit easier when the alkalinity is close to 100
4. Get the pH close to 7.4, at least between 7.2 and 7.6
   • now check the pH of your water
   • if it’s above 7.6, you need to start the circulation and add some dry acid
   • that’s the same chemical as for reducing the alkalinity
   • it’s a bit like magic that when the alkalinity is close to 100, you can add dry acid to reduce the pH and the alkalinity doesn’t move. It’s like the alkalinity level of 100 is some sort of stable state.
   • if the pH is below 7.4, you need to add some Borax. This time it’s different to the chemical used to raise alkalinity. If you use Sodium Bicarbonate to raise pH, you’ll raise the alkalinity as well and everything will get out of whack.
   • after 30 minutes, test the pH again
   • repeat until the pH is around 7.4
   • it’s good to double-check that the alkalinity is still ok – it’s very important that the alkalinity states near 100 for the state of the pool (if the alkalinity is significantly out for some reason, go back to the start)
5. Add Sodium Bromide – a key step!
   • now the magic chemical that makes all the difference
   • this ensures you have sanitised water from the very start
   • you need half an ounce for each 100 gallons of water in your hot tub
   • my hot tub holds 440 gallons of water and I put in 2.5 ounces of sodium bromide
   • get the circulation going and add the powdered sodium bromide
6. Add Bleach
   • now a little chlorine (bleach) to get everything activated
   • you need about 5 tablespoons of bleach (assuming the bleach is 5% concentration) for each 100 gallons of water
   • adjust the amount depending on the concentration of your bleach
   • I find the actual amount is not so important and just approximating the amount seems to work fine
   • you can add this bleach quite soon (just a few minutes) after adding the sodium bromide, while the circulation is still running
7. Add the bromine tablets
   • Now you add the bromine tablets for the normal running of the hot tub – follow the instructions that came with the hot tub
   • in my case, the tablets go in the filter assembly
   • sometimes they might go in a floating dispenser
8. Turn on the heating
   • now you’re all done with the initialisation, and you can turn up the heating to the desired temperature and close up the hot tub

Ongoing Maintenance

Generally, the more you test the water in the hot tub the better. I tend to test it every 2-3 days, and I always test it the day after it has been used. If the alkalinity if quite close to 100, it tends to be very stable and only changes slowly. Some people say you only need to test this once a week, but I test it every time I test the water because, if it’s starting to drift off, it’s good to know early.

If the alkalinity is between 80 and 120, I don’t worry about it and only worry about the pH and bromine level. If the alkalinity is outside this range, then nothing else matters, you have to return the alkalinity to close to 100 before doing anything else. If it’s below 80, add sodium bicarbonate. If it’s above 120, add dry acid. Add the chemicals while the hot tub circulation is running, wait 30 minutes and test it again to see the change. Keep adjusting until it’s close to 100.

Next check the pH and the bromine level. If the pH is between 7.2 and 7.6, just leave it alone. If it’s outside this range, then add Borax to raise it and dry acid to lower it. If the bromine level is outside the range of 1.5-2.5, then increase the size of the opening in the tablet holder to raise the level, or close it a bit to lower the level.

If the bromine level is really low (less that 0.5) it’s probably a good idea to get it up quickly. A splash of bleach is a good idea and adding some bromine granules can do the trick. Of course, check you have enough tablets in the dispenser and open up the size of the slots where the bromine is released.

If the bromine level is very high (above 4.0), then the best way to get the level down is to lift the lid and run all the pumps and jets as much as possible. It’s not a great idea to get into a hot tub with a very high bromine level – too much chemical exposure. Get the level down before getting in.

If you check the chemicals at least every 2-3 days and take quick action when they start drifting away from the good balance points, you’ll find the water will stay clear and inviting for quite a long time. It’s well worth the care and attention to save work in the long run, and give you a continuous opportunity to enjoy your bromine hot tub.

Related Links – Bromine Hot Tub

• Bromine or Chlorine? – https://www.hottubsuppliers.com/bromine-or-chlorine
• Pooltester kit – avoiding Bromine Hot Tub nightmares
• Palintest on DPD testing – https://www.palintest.com/content-hub/a-guide-for-dpd-testing-in-pools-and-spas/
• I learnt a lot from this forum – https://www.poolspaforum.com/forum/index.php?/topic/26324-whats-the-step-by-step-to-bromine-treatment/