Chlorine, bromine or active oxygen: which hot tub water treatment?

Why hot tub water needs treating

Hot tub water is warm, around 37 °C, and its volume is small compared with the number of bathers: a few hundred to a few thousand litres, against dozens of cubic metres for a swimming pool. It is an environment where micro-organisms grow quickly. Filtration catches particles, hair and cream residue, but it does not destroy bacteria: that is the sanitiser's job.

Water treatment therefore protects the bathers, but also the hot tub itself. Water that is too acidic or too hard damages the seals, the pumps and the heater.

First, the pH

Before talking about chlorine or bromine, you need the right pH, between 7 and 7.4. Too low, and the water becomes aggressive for the equipment and irritates the skin; too high, and it scales up and the sanitiser loses much of its effectiveness. It is measured with test strips or an electronic tester, and corrected with a "pH plus" or "pH minus" product.

Alkalinity (TA) acts as a buffer: when it is properly set, the pH stays stable from one week to the next. If your pH keeps moving, alkalinity is often what needs correcting first.

Chlorine

This is the most widely used sanitiser. It acts quickly, is available everywhere and is easy to measure.

• Strengths: effective, economical, easy to dose, handy for quickly clearing cloudy water.
• Things to watch: by combining with impurities, it forms chloramines, which cause the so-called "swimming pool" smell and irritation; it breaks down faster in hot water.

For a hot tub, use specific products, as granules or slow-dissolving tablets suited to small volumes. Always follow the dosage given by the product manufacturer.

Bromine

Bromine is often preferred for hot tubs.

• Strengths: it remains effective in hot water and over a wider pH range; its smell is more discreet than chlorine's.
• Things to watch: it costs a little more, dissolves slowly (tablets in a floating dispenser or a brominator) and is slower to correct cloudy water.

One important rule: never mix chlorine and bromine. If you change sanitiser, drain the hot tub.

Active oxygen

Active oxygen appeals to those who want to avoid chlorine-based products.

• Strengths: no smell, water that is pleasant for the skin and eyes.
• Things to watch: its effect does not last as long, it is usually used with an activator, and it has to be dosed more often, especially when the hot tub is used a lot.

It suits moderate, regular use, with water that is monitored closely.

The UV lamp: an addition, not a replacement

Most of our hot tubs, from the 2-seater Samana to the 8-seater Santiago, can be fitted with an optional AquaPure UV lamp (€200); the "Options" section of their product page says so. Ultraviolet light destroys some of the micro-organisms as the water passes through and reduces the amount of sanitiser needed. It does not replace chlorine, bromine or active oxygen, though: the water in the tub must always contain an active sanitiser.

Comparison

Treatment	Strengths	Things to watch
Chlorine	Fast, economical, easy to measure	Smell and irritation if the water is poorly balanced
Bromine	Stable in hot water, discreet smell	More expensive, slower to correct
Active oxygen	Odourless, gentle on the skin	Shorter effect, more frequent dosing
UV lamp (addition, optional)	Reduces the amount of products	Never enough on its own

Family hot tub, swim spa, commercial hot tub

The principle stays the same, but volume and use change the routine.

• Small hot tub: a 2 or 3-seater holding 360 to 680 litres reacts quickly to the slightest addition of product. Dose precisely and test more often. See our 2 and 3-seater hot tubs.
• Swim spa: the 6,400 litres of the Ocean swim spa make the water more stable, but each correction needs more product.
• Hot tub open to guests: in a holiday let, a B&B or a hotel, heavy use calls for enhanced filtration, such as the sand filter of the FX Pro, and hygiene rules to follow. See our commercial hot tubs.

Getting started after filling

1. Fill the hot tub and start the filtration and heating.
2. Test and adjust the alkalinity, then the pH.
3. Add the sanitiser you have chosen, according to the instructions, with a start-up treatment if the product manufacturer recommends one.
4. Test again the next day before the first soak.

After that, the weekly routine takes about ten minutes: checking the pH and sanitiser, rinsing the filters. It is detailed in our guide Hot tub maintenance. A complete drain every three to four months, more often if the hot tub is used a lot, starts again with fresh water.

Mistakes to avoid

• Mixing products from different families, or pouring them in together: add them one at a time, into the water, with the filtration running.
• Correcting the sanitiser before the pH: without the right pH, the products work poorly.
• Forgetting the filters: a clogged filter makes the water cloudy whatever the treatment.
• Storing products just anywhere: keep them dry, cool, out of reach of children, each in its original packaging.

Which treatment should you choose?

For regular family use, bromine is often the most comfortable. Chlorine suits those who want a simple, economical treatment and check their water every week. Active oxygen is for those who want to avoid chlorine-based products and accept more frequent dosing. In every case, use the Tropic Spa approved maintenance products and filters that your advisor recommends for your model: this is a condition of the warranty (see Our warranties), and poorly balanced water can damage the equipment.

Planning your project? Request your quote: your advisor will also tell you about the filtration equipment of each model.