Spa pool treated with sanisers

Spa Sanitiser: How To Keep Your Spa Water Clean [Guide]

If there’s one way to keep your hot tub clean, it’ll be with good ol’ spa sanitiserBecause without it, your prized hot tub will quickly turn into a cesspool of grotesque gunk, and we think you should probably leave that sort of science experiment up to actual scientists.

Although the thought of spa sanitation might turn your brain into a whirlpool, this guide is going to put you on the straight and narrow. So if you’re a new spa owner looking for the best spa sanitiser or your dirty spa water has you stumped, we’re here to help you clean up this mess.

In this guide, we’ll cover:

Let’s dive in.

What is a Spa Sanitiser?

A spa sanitiser is essentially a chemical compound based on chlorine or bromine. Besides, it comes in different dispensing methods: tablets, granules and even as a filtration system. Even though the outcome of bromine and chlorine are very similar, they still have their differences, which we will soon see.

A spa sanitiser has one main objective: to kill harmful bacteria and organisms before they multiply and build up in your spa water, causing havoc in every nook and cranny.

How chlorine as a spa sanitiser works

Chlorine molecules follow a process called oxidation, which means they’re a sneaky spa sanitiser.

When it’s added to your spa water, the chlorine molecules combine with bacteria and steal their electrons, subtly deeming them powerless.

After chlorine has taken its loot from one bacteria, it changes into a waste product known as chloramine. The smelliness that most of us mistake for chlorine is actually the smell released by chloramines, and you won’t want that to stick around.

Chlorine shock (sodium dichlor) oxidizes the chloramines into the air, or in other words, gases them out. Good riddance. Once its life cycle is complete, a new batch of chlorine is introduced, and the cycle starts afresh.

Chlorines attack bacteria only once, and then become ineffective chloramines, so they smell and they’re useless.

How bromine as a spa sanitiser works

Bromine molecules follow a process called ionization, which means they’re an aggressive spa sanitiser.

When it’s added to your spa water, bromine molecules combine with bacteria and rip apart their chemical bonds, basically annihilating them. After bromine has eradicated the invader, it leaves behind a by-product known as bromimines.

Unlike chlorine, bromine continues to work again and again, you’ll just need to oxidize the by-product, bromimine, with non-chlorinated (potassium monopersulfate) shock treatment, so they don’t build up. Not only are bromine molecules hard workers, they also don’t tend to smell as much.

What Is The Best Spa Sanitiser?

All things considered, the best spa sanitiser has to be bromine.

A bottle of Bromine working as spa sanitiser

But chlorine is also a strong contender. It just depends on your preferences and where you’ve put your spa. Check out the pros and cons between the two in the table below:





  • bromine molecules can be reused. 
  • less smelly.
  • more stable in higher temperatures.
  • best spa sanitiser for sensitive skin. 
  • lower pH. 
  • faster-acting.
  • cheaper.
  • easy to dose.
  • breaks down slower from UV light from the sun. 



  • slower-acting.
  • more expensive.
  • one dispensing method.
  • breaks down quickly from UV light from the sun. 
  • chlorine molecules cannot be reused. 
  • more smelly. 
  • less stable in higher temperatures. 
  • worst spa sanitiser for sensitive skin. 
  • higher pH. 

You can probably see now how bromine comes out on top. For those of you leaning more towards chlorine, we’ve still got a few other suitable chlorine options for you to choose from in the section coming up next.

What Should I Use To Sanitise My Hot Tub?

There are plenty of spa sanitiser options to use in your hot tub.

If you want to use chlorine

Like we said, plenty of options swimming around here. First up, the tablets and granules:

Missing your lithium-based chlorine?

Back in the good old days, lithium sanitiser was flying off the shelves. It was fast dissolving, and easy to apply to the pool. As it was a little more pure than sodium based spa sanitiser it meant the water in the spa could last a little longer before being changed.

But those days came to an end. The price of lithium was too high to be used in a humble sanitiser, now that products such as batteries have become increasingly popular. Everyone had to make a change if lithium based chlorine had always been their go to.

But good news! Lithium is coming back! Watch this space or check with your pool shop if you prefer lithium sanitiser and want to change back.

If you want to use bromine

As for bromine, it only comes as a spa sanitiser tablet. But that’s a good thing. Unlike granules, you won’t need to fumble around with measuring and mixing, turning your serene spa area into a laboratory. You’ll just need the bromine tablets and the feeder

Don’t let the limited options of bromine put you off, just remember that bromine is the best spa sanitiser to use.

Bromine works a little differently from chlorine in the spa. With bromine, you create a “bromine bank” in the water, and then only need to top up the bank. That means once you’ve got the right amount of bromine in the water, you can reduce the number of tablets you use.

Unlike chlorine which gets consumed treating the water in the spa, bromine will go from an active to an inactive state while staying in the water. You reactivate the bromine when you shock-dose the spa with chlorine.

Bromine, chlorine, whichever one you stick with, the main takeaway is to choose the most suitable option for your circumstances and apply them properly. Remind to read the manufacturer’s instructions, and always stay safe when adding them into your spa water.

Tips On Keeping Your Spa Water Clean

Sanitiser alone can’t fight off the everlasting battle between dirty and clean. It does a good job at keeping bacteria at bay, but it’s up to you to give spa sanitiser a fighting chance.

To prevent your spa getting dirty, follow through with these few steps below. And if it’s already grubby, it’s never too late to get your spa cleanliness on track.

Give your hot tub a deep clean

Refilling a spa pool with water

Refill your tub with fresh, filtered water in these circumstances:

  1. When your sanitiser levels aren’t rising.
  2. Your spa is dirty beyond repair.
  3. Every three months or as your pool shop recommends.

Take the opportunity to deep clean the filters with cleaning chemicals and scrub down your spa while it’s empty, removing any scum that is otherwise difficult to remove.

Clean where you can’t see

Just because you can’t see it doesn’t mean it’s not there. Some of the worst spa water problems can be due to dirty pipes. When biofilm starts to build up in a spa’s piping, bacteria is more likely to build up too. Keep your pipes clear with pipe cleaner, A regular use cleaner to avoid build up in your pipes.

Then there’s one other spa part that you’ll need to draw your attention to: the filters. Your poor pool filters work hard night and day clearing out contaminants in your spa water. In order for your filters to keep your spa water clean you’ll need to keep them clean.

Give them a brief hose down once a fortnight and a deep clean with a filter cleaner like Focus Filter Cleaner & Degreaser every few months.

Shock your spa regularly

You’ll need to remove chloramines or bromimines from your spa water at least once a week to maintain clear spa water. The options for shock-dosing are:

Always test for chlorine or bromine levels and top up as needed after a shock treatment – just in case.

Balance your spa chemistry

Before you even think about sanitising your spa, you’ll need to test the spa water for pH, alkalinity, and calcium hardness.

Then you can adjust as needed with these handy helpers:

Bromine and chlorine molecules are fussy, and will work best in water that has been balanced first. If the pH levels are imbalanced, spa sanitisers won’t attack contaminants and you could run into a foamy water problem.

If you’ve got foamy water and you’re strapped for time, you can always use an anti-foam, a quick fix for clearing foam from spa water.

It’s not practical to use anti-foam continuously. It’s cheaper and safer to just keep your spa chemistry balanced.

Shower before using your spa

If you’re wondering why your spa water is going cloudy, this could be the answer. The oils from skin and hair products can contaminate spa water and turn it into a murky mess.

Your filter can’t always pick up what comes off of our bodies. So, it’s best to wash oils off if you want your spa water to remain clear.

Just keep sanitising your spa

If you use bromine as a spa sanitiser, keep the dispenser floating around and take it out when you’re using the spa. Bromine levels in your spa need to remain between 3-5ppm.

As for chlorine, test the levels three times a week and shock at least once a week. Add additional chlorine tablets or granules when the levels are too low.

Chlorine levels in your spa need to remain between 1-3ppm.

Cover your hot tub

The air carries tiny particles, debris, and dust that can land in your spa pool and begin to build up if you regularly leave the lid off. So keep that lid on, unless of course you’re in your spa. This will reduce your heating costs too!

Keep on top of all of these tips and your spa will remain clean and clear! 

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.

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