How to clean a hot tub: filters and surfaces

The filter gets rinsed every 30 days and replaced after one or two years. Surfaces are cleaned when the water is out, not while it is in. The rest of routine maintenance takes about a quarter of an hour a week, and most of that is running water over a cartridge.

I'll take you through how it is done, in what order, and how long each job actually takes. You'll find the intervals one by one, what you need, and the three mistakes I have seen ruin more cartridges than heavy use ever has.

All the intervals in one place

Maintaining a hot tub is not one job: it is four jobs on four different timescales. Confusing them is why it feels like constant work to some people and like nothing at all to others.

Every week you check the sanitiser and drop a fresh bromine tablet into the skimmer. Slow-release 20 gram tablets cover 30 to 40 days of water treatment, but the dose is renewed weekly: that is the rhythm that keeps the level steady instead of letting it swing.

Every 30 days you take the cartridge out and rinse it. This is the most important of the four, and the one most often skipped.

Every 4 to 6 weeks, on a tub under 2 cubic metres, you change the water. At small volumes a refill costs less than the chemistry needed to hold the water in good condition for longer: it is a decision about cost, not about hygiene.

Every 1 to 2 years you replace the cartridge. Sooner only if it is damaged or holed.

On top of these there is cleaning the surfaces, which has no interval of its own: it happens when the tub is empty, so it follows the water change.

How to wash the cartridge, and why the jet goes top to bottom

Take the cartridge out of the skimmer and rinse it with clean water at medium pressure, directing the jet downwards along the pleats. This is not a cosmetic detail: the pleats collect dirt by gravity, and a jet from below drives it further in instead of flushing it out.

Medium pressure, not a pressure washer. The cartridge is pressed paper: too violent a jet spreads the pleats open, and from that point on it filters worse, even though it looks cleaner than before.

It then needs to dry completely in the air before going back in. A cartridge refitted wet holds moisture between the pleats and becomes the most hospitable place in the tub for exactly what you are trying to remove.

If you keep a second cartridge as a spare the job gets easier: you fit the dry one and let the other dry at its own pace. Our paper cartridges cost € 145 and come in different sizes, because the diameter varies from model to model: our mod. 3 is 14 cm across and 20 cm tall. Measure the one you have before ordering a second. Compatible sizes are in the hot tubs catalogue. The full procedure, with the tolerances for your own unit, is in our support note on water treatment.

When the cartridge genuinely needs replacing

The stated life is one to two years with proper maintenance, and where you land in that range depends almost entirely on how many rinses it has had. A cartridge washed every month reaches the end of the second year; one washed whenever somebody remembers clogs irreversibly long before that.

There are three signs that mean replace it now, without waiting for the calendar: the cartridge is holed or torn, the pleats are deformed and will not sit back in position, or water quality deteriorates noticeably while the chemical readings stay correct.

The last one is what confuses people most. If the bromine is fine and so is the pH, but the water stays cloudy, the problem is mechanical rather than chemical: you are adding product to a filter that no longer holds anything back. That is the moment when people spend money on sanitiser instead of on a spare that costs a few euros.

Surfaces: clean them with the tub empty

The shell gets washed when the water is out, straight after a change. A soft cloth and water are enough for routine cleaning; limescale needs a specific product, applied to a dry surface rather than a wet one.

What you must not use on acrylic is a short list and it deserves respect: no abrasive pads, no solvent-based products, no household cleaners. Acrylic scratches, and scratches are not a cosmetic problem: they become the place where dirt settles and never comes out again.

The floor of the tub is where everything the filter misses ends up, meaning grit, bits of leaf and hair. It comes out with a spa vacuum, which works with the tub full: ours costs € 133 and runs on a battery, so there is no mains power near the water. It is a one-off cost that works out cheaper than bringing a water change forward.

The thermal cover gets cleaned on both faces with a cloth and plain water. Underneath, where the vapour touches it, a film builds up that ends up back in the water every time you open it.

The jets and the pipework nobody looks at

The internal pipework is the part of the system you never see, and it accumulates residues of creams, oils and body products. It is also why some tubs foam despite the water being fresh.

Cleaning is done with a dedicated pipe sanitiser, and it has to happen before draining, not after: the product needs to circulate through the system with the pumps running, and then everything drains together. Doing it after the tub is empty means cleaning empty pipes, which is a job with no point.

You do not need one bottle a year: a pack of sanitiser, € 54 in our catalogue, covers several cycles. The real running cost is the sanitiser itself, meaning slow-release bromine tablets at € 79 a pack, which at one tablet a week covers a good six weeks.

It is the task people do least often and the one that solves the most apparently inexplicable problems. If your tub is a year old and you have never done it, that is probably why your bromine does not last as long as it should.

The three mistakes I see most often

The first is skipping the shower. Sweat, sun cream, traces of shower gel and detergent from your swimwear all go into the water with you. It is not a question of personal cleanliness: those residues are organic matter, and organic matter is precisely what consumes the sanitiser. Showering before getting in is one of the measures set out in the World Health Organization's Guidelines for safe recreational water environments, Volume 2 (2006), which devotes a chapter to controlling the pollutant load bathers bring with them. It is the cheapest maintenance there is, and it applies to a domestic hot tub as much as to a public pool.

The second is swimwear washed with fabric softener. The fabric holds it and releases it into the tub, where it turns into foam. If your water foams and you cannot work out why, look at how you wash your swimwear before hunting for a fault in the system.

The third is adding product without measuring. The pH belongs between 7.0 and 7.6, and outside that window the sanitiser loses its effectiveness while remaining present in the water. Above 7.6 the bromine is there but doing very little: anyone who adds more is spending money on a result that will not come, and the fix is to correct the pH, not to raise the dose.

The weekly quarter of an hour, in order

Laid out in sequence, the recurring work looks like this. You test the pH and the sanitiser, and correct only if you are outside the 7.0 to 7.6 window. You drop the bromine tablet into the skimmer. You run the vacuum over the floor if you can see deposits. Once a month you add the cartridge rinse, which is another ten minutes plus drying time.

The water change every 4 to 6 weeks is the only job that takes half a day, and only because filling is slow. The cost of the water itself for a hot tub is on the order of one and a half euros: the full calculation, with volumes and annual running costs, is in the guide on hot tub water costs.

If the water has already gone cloudy or started foaming, it pays to work out why before doing anything: the causes and the fixes, in order of how easily you can check them, are in the guide on cloudy and foamy hot tub water.

Frequently asked questions

How often should you clean a hot tub filter?
Every 30 days, rinsing it with clean water at medium pressure, working downwards along the pleats. It has to dry completely in the air before going back in. If the tub is used by several people or more often than average, shorten the interval rather than increasing the sanitiser.

How long does a hot tub filter cartridge last?
One to two years with a regular monthly rinse. Replace it sooner if it is holed, if the pleats are deformed, or if the water deteriorates while pH and sanitiser readings are correct: in that case the problem is the filter, not the chemistry.

Can you clean a hot tub filter with a pressure washer?
No. The cartridge is pressed paper and high pressure spreads the pleats permanently: from then on it filters less, even if it looks clean. You want water at medium pressure, like a garden hose.

Why is my hot tub foaming?
Almost always organic residues: shower gel, creams, and above all fabric softener held in swimwear. Less often it comes from internal pipework that has never been sanitised, where residues build up and return to the water every time the pumps start.

What should you use to clean acrylic surfaces?
A soft cloth and water for routine cleaning, a specific limescale product on a dry surface for deposits. Never abrasive pads, solvents or household cleaners: they scratch the acrylic, and dirt settles permanently in the scratches.

Do you need to drain the tub to clean the pipework?
The sanitiser has to circulate with the tub full and the pumps running, and only then do you drain. Cleaning the pipes after draining achieves nothing, because the product has no way of passing through them.

What to do, in order

What matters, in sequence.

1. Rinse the cartridge every 30 days, jet downwards along the pleats, and let it dry completely before refitting it.
2. Test the pH weekly and keep it between 7.0 and 7.6: outside that window the sanitiser is present but not working, and adding more will not help.
3. Drop the bromine tablet into the skimmer weekly, without waiting for the water to change appearance.
4. Shower before getting in: it is the single thing that most reduces the organic load in the water, and it costs nothing.
5. Sanitise the pipework once a year, with the tub full and the pumps running, before you drain.
6. Replace the cartridge after one or two years, or immediately if it is holed or if the water deteriorates while the chemical readings are correct.

The most common mistake is putting off the monthly rinse and compensating with more sanitiser. It does not work, because the problem becomes mechanical: a clogged filter holds nothing back, and the product you add is working on water that keeps getting dirtier. If the tub is new or you have just inherited one, the concrete step is to put the first rinse in the calendar: maintenance almost always fails through forgetfulness rather than difficulty.

If you have a question about water treatment on your own model, our customer support will answer with your unit's spec sheet in front of them, and compatible consumables are in the hot tubs category. Who we are and what we do is on the about us page.

Catalogue figures in this guide (capacity, dimensions and prices) are read from the product pages and update with the catalogue: what you see is the current value. Intervals, doses and frequencies are general guidance for average domestic use and do not replace the manual for your model or the instructions on the chemical products you use. If you are unsure about water treatment, refer to technical support.