Water treatment: How to keep your hot tub water clean

Clean and healthy water is a fundamental requirement for a safe spa experience. Hot water is an ideal environment for the proliferation of bacteria, which can cause rashes and other infections, so it is essential that you keep your hot tub water disinfected and slightly disinfectant.

There are several methods of chemical disinfection, each with its own advantages and disadvantages.

First of all, it is very important to know the volume of water in your spa in order to correctly dose your products.

Additionally, and we can never say it enough, you must absolutely be clean when you get into a spa, because the more dirt or sweat residues you bring into the spa, the more your disinfectant will react with these residues and be neutralized. In other words, your disinfectant would soon stop being effective, and that's where the dreaded biofilm comes in.

These explanations are here to help you make the best choice between chlorine, bromine, and active oxygen, according to how often you use your spa, so that you can disinfect your spa perfectly.

Please note these explanations only include treatments for domestic use.

Chlorine: instantaneous and long-lasting

It is the most commonly sold treatment on the market.

It is more accurate to talk about free chlorine (or HOCl), which corresponds to the dissolution of pure chlorine (this is the one you find in the form of granules or effervescent tablets) in your water. It has almost no smell, but leaves an impression of cleanliness and freshness. It is the quality of this free chlorine that you must test.


  • Persistent: remains active for several days in a clean spa
  • Takes effect immediately and is very effective, even at low concentrations
  • Cheapest disinfectant available
  • Reacts very quickly with other contaminants in the water, especially perspiration
  • Results in the formation of chloramines, and the "free" chlorine is transformed into "combined" chlorine and releases the strong unpleasant smell of chlorine
  • Drastically decreases the disinfecting capacity of the remaining free chlorine
  • pH sensitive, and loses its effectiveness if the pH is above 7.6

Feel free to follow our tips on chlorine treatment!

Bromine treatment: long-lasting... but slowly dissolving

The (free) bromine treatment (tablets) is very similar to chlorine, since it has the same disinfection qualities.


  • Persistent
  • Is not pH sensitive and odourless
  • Reacts with contaminants in water (especially perspiration). The "combined" bromine is then formed. This combined bromine retains some of its disinfectant capacity
  • Recyclable: it is possible to reactivate part of the combined bromine into free bromine by adding active oxygen
  • Dissolution that takes several days (time varies depending on spa's water flow) in contrast to chlorine's immediate dissolution. The use of your spa needs to be anticipated.
You may find that slow dissolution is actually an advantage. If your spa is used regularly and consistently, bromine treatment can help keep the water healthy with less control and attention... but it requires some practice and anticipation.

Feel free to follow our tips on bromine treatment!

Active oxygen / Non-Chlorine Shock treatment: No odour and occasional

Non-chlorine shock or "Monopersulfate" (also marketed as "Active Oxygen") is a powerful oxidizing agent and has the same sanitizing properties as chlorine or bromine. It kills bacteria and eliminates residues left behind by bathers, like sweat, or sunscreen. Some people rely on active oxygen (tablets) or chlorine-free shock (powder) as an alternative to chlorine or bromine. We don't recommend this unless you know that you're allergic to both chlorine and bromine; it is efficient, but it is much better to use it as an occasional shock treatment.


  • Softer than chlorine or bromine
  • Odourless
  • Leaves no harmful residues. Lessens the risk eye or skin irritation


  • Very unstable, meaning that its anti-bacterial effect doesn't last very long
We recommend active oxygen in one in a "shock" treatment (hence its name). You must "shock" the water once a week or as soon as the chlorine or bromine level is at zero. Active oxygen makes it possible to destroy part of the combined chlorine, and to reactivate part of the combined bromine to transform it back into free bromine.

The problem with using unstabilised chlorine as a shock treatment

You may be wondering "is there a substitute for the active oxygen / non-chlorine shock treatment?". There is a chlorine shock treatment, but the problem with shocking agents that contain chlorine is that the efficient products are often unstable and dangerous to stock and to use.

That is why se do not sell stabilizer-free chlorine products.

It is safer to use stable chlorine in granules ("dichlorine"), but the downside is that you need to add a lot and wait for 24 to 48 hours for the water to be safe again. Whereas with stabilizer-free chlorine shock powder, you can add one or two doses and your water will be clean in about five minutes... BUT this product is more dangerous than other cleaning products used in spas. In particular, it may release chlorine gas explosively after contact with several types of liquids, and it requires special precautions for storage and transport.

We prefer to offer Non-chlorine shock powder, which is used in a similar way, even if it is a little less powerful, and which is much easier to sell at a distance.

The best disinfectant method would be to use mainly the chlorine or bromine treatment, and add active oxygen or non-chlorine shock powder after swimming to oxidize sweat.

More information on water treatment

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