You’ve had your hot tub for six months now. Every week you’re fiddling with test strips, dumping in chlorine granules, waiting 20 minutes before getting in, and wondering why it still smells like a swimming pool. Your mate Dave got a UV system fitted and claims he barely touches chemicals anymore. You’re sceptical, but also tired of the chemical juggling act.
Hot tub sanitation doesn’t have to be a constant battle. Modern sanitiser systems — UV, ozone, and salt chlorine generators — can automate most of the work and slash your chemical usage. But they’re not magic, they’re not cheap, and they’re not all suited to every setup. Here’s an honest comparison of what actually works in UK hot tubs.
In This Article
- Why You Still Need a Residual Sanitiser
- UV Sanitiser Systems
- Ozone Systems
- Salt Chlorine Generators
- Head-to-Head Comparison
- Which System Suits Your Hot Tub
- Running Costs Breakdown
- Installation and Retrofit
- Combining Systems
- Maintenance Requirements
- Common Myths About Alternative Sanitisers
- Frequently Asked Questions
Why You Still Need a Residual Sanitiser
Before we get into the systems, this is the single most important thing to understand: no UV or ozone system eliminates the need for chemical sanitiser entirely. They reduce how much you use, sometimes by 50-80%, but you still need a residual sanitiser in the water to kill bacteria between filtration cycles.
How Traditional Sanitisation Works
Chlorine or bromine sits in the water constantly, killing bacteria on contact. When someone gets in, they introduce contaminants — skin cells, sweat, body oils, the odd bit of garden debris. The sanitiser attacks these immediately, which is why you need a measurable level in the water at all times.
What Alternative Systems Actually Do
UV and ozone systems sanitise the water as it passes through the plumbing during filtration. They’re brilliant at killing pathogens in the pipe — 99.9% effective in most cases. But they don’t leave anything behind in the water itself. Once the water returns to the tub, it’s clean but unprotected until the next filtration cycle.
That’s why even the best UV or ozone system needs a small amount of chlorine or bromine as backup. Think of it as a belt-and-braces approach: the system does the heavy lifting, the residual chemical handles anything between cycles.
UV Sanitiser Systems
UV-C light has been used in water treatment for decades — municipal water supplies, swimming pools, aquariums. Hot tub UV systems work on the same principle, just scaled down.
How They Work
Water passes through a chamber containing a UV-C lamp (typically 254 nanometres wavelength). The UV light damages the DNA of bacteria, viruses, and algae, preventing them from reproducing. The water exits the chamber sanitised and returns to the tub.
Best UV Systems for UK Hot Tubs
- Aqua Spa UV-C System — about £300-400 installed. The most common retrofit option for UK hot tubs. Compact unit that fits into existing plumbing with minimal modification.
- ClearRay by Jacuzzi — £200-350 for the replacement bulb assembly. Factory-fitted on many Jacuzzi models. If your tub already has one, you’re sorted — just replace the bulb annually.
- AquaFinesse UV-C — about £350-450. Higher-output system for larger tubs. The quartz sleeve is easier to clean than some competitors.
Advantages of UV
- No chemical byproducts — UV doesn’t add anything to the water
- Effective against chlorine-resistant pathogens — kills Cryptosporidium and Giardia that chlorine struggles with
- Low running cost — the bulb uses about 20-40 watts, adding roughly £5-10 per year to your electricity bill
- No smell or taste — the water feels noticeably cleaner and less chemical
Limitations of UV
- Only works during filtration — water sitting in the tub between cycles is unprotected
- Bulb replacement needed — typically every 12 months, costing £40-80 depending on model
- Quartz sleeve cleaning — calcium deposits reduce effectiveness, needs cleaning every 3-6 months
- Flow-rate dependent — if water moves through the chamber too fast, exposure time drops and effectiveness decreases
Ozone Systems
Ozone (O₃) is one of the most powerful oxidisers available. It’s the same compound that makes the air smell fresh after a thunderstorm — and it’s been used in European water treatment since the early 1900s.
How They Work
An ozone generator creates O₃ by either passing air through a corona discharge cell (CD) or exposing it to UV light. The ozone is then injected into the hot tub plumbing via a venturi injector or mixing vessel. It oxidises organic matter on contact, breaking down bacteria, viruses, oils, and other contaminants.
Corona Discharge vs UV Ozone Generators
- Corona discharge (CD) — the better option. Produces more ozone per hour, lasts longer, works better in humid conditions. About £250-500 for a quality unit.
- UV ozone generators — cheaper (£100-200) but produce less ozone and the UV bulb degrades faster in humid environments. Many budget hot tubs come with these pre-installed.
Best Ozone Systems for UK Hot Tubs
- DEL Ozone MCD-50 — about £250-350. Corona discharge unit that’s become the industry standard for mid-range hot tubs. Reliable and well-supported in the UK.
- Balboa Ozone Generator — about £150-250. Common factory-fit option. If your tub has Balboa controls (many UK brands do), this slots straight in.
- Prozone CSS-7 — about £400-550. Top-tier CD unit with higher output. Worth it for tubs over 1,500 litres or heavy use.
Advantages of Ozone
- Powerful oxidisation — breaks down body oils, lotions, and organic matter that chlorine has to work overtime to handle
- Reduces chloramine formation — fewer of the byproducts that cause that unpleasant “pool smell”
- Reduces chemical usage by 50-80% — depending on bather load and usage frequency
- Extends filter life — cleaner water means less gunk trapped in filters
Limitations of Ozone
- Short-lived — ozone reverts to oxygen within 20-30 minutes, so there’s no residual protection
- Can degrade rubber components — ozone attacks some gaskets, headrests, and pillows over time. Check your tub manufacturer’s compatibility
- Needs good mixing — if the ozone doesn’t mix properly with water, it off-gasses without doing its job
- CD units need replacing — typically every 3-5 years (the corona discharge cell wears out)
Salt Chlorine Generators
Salt systems have dominated swimming pools for years and are now increasingly popular in hot tubs. They work differently from UV and ozone — instead of reducing chemical use, they automate chlorine production.
How They Work
You add about 2-3kg of salt to the hot tub water (far less than a swimming pool). The water passes through an electrolytic cell that splits the salt (sodium chloride) into sodium and chlorine. The chlorine sanitises the water, then recombines with sodium to form salt again. It’s a continuous cycle.
The result is a consistent chlorine level without you ever handling granules, tablets, or liquid chlorine.
Best Salt Systems for UK Hot Tubs
- FreshWater Salt System by Hot Spring — about £500-700 installed. Factory-fitted on Hot Spring models, retrofit available for others. The titanium cell lasts about 4 months and costs £30-40 to replace.
- AquaPure by Jandy — about £400-600. Swimming pool system adapted for hot tubs. Higher output than most, which suits larger tubs.
- Chloromatic — about £350-500. Australian-designed, increasingly available in the UK. Compact cell suits tighter plumbing configurations.
Advantages of Salt Systems
- Fully automated sanitation — set it and forget it. The system maintains chlorine levels without you adding anything
- Softer-feeling water — low salt concentration makes water feel silkier on skin. Many users report less skin irritation
- Lower ongoing chemical costs — salt is cheap (about £3-5 for a 25kg bag), and you add it rarely
- No chlorine handling — no storing granules, no measuring, no waiting after dosing
Limitations of Salt Systems
- Higher upfront cost — the most expensive option at £350-700+ installed
- Cell replacement — electrolytic cells wear out every 3-12 months depending on model, costing £30-80 each
- Salt can corrode metal — stainless steel jet fittings, heating elements, and some plumbing components can corrode faster. Check your tub’s warranty covers salt use
- Still produces chlorine — if you’re trying to avoid chlorine entirely, this isn’t the answer. It just automates the process
Head-to-Head Comparison
Here’s how the three systems compare across the factors that actually matter for UK hot tub owners:
- Chemical reduction — UV: 30-50% less. Ozone: 50-80% less. Salt: no reduction (automates chlorine instead)
- Upfront cost (including installation) — UV: £300-500. Ozone: £200-550. Salt: £400-700
- Annual running cost — UV: £50-90 (bulb + electricity). Ozone: £20-40 (electricity only, cell every 3-5 years). Salt: £60-120 (cells + salt)
- Installation complexity — UV: moderate (plumbing modification). Ozone: easy (most tubs have a port). Salt: moderate to complex
- Maintenance effort — UV: clean sleeve quarterly, replace bulb annually. Ozone: minimal. Salt: replace cell periodically, monitor salt level
- Water quality improvement — UV: noticeable. Ozone: significant. Salt: softer feel, consistent chlorine
Which System Suits Your Hot Tub
Weekend Users (1-2 times per week)
Ozone is your best bet. The oxidisation keeps water clean between uses, and the minimal maintenance suits a hands-off approach. Add a small amount of bromine weekly and you’re done.
Daily Users
A salt chlorine generator makes the most sense. The automated chlorine production keeps up with heavy bather loads without you constantly adjusting levels. The higher upfront cost pays back quickly through saved time and chemicals.
Chemical-Sensitive Users
UV combined with a low bromine residual gives you the cleanest, least chemical water. UV doesn’t add anything to the water, and you can run the bromine level at the absolute minimum (1-2 ppm versus the normal 3-5 ppm).
Budget-Conscious Buyers
A UV ozone generator (the cheaper UV-based type, not corona discharge) comes pre-installed on many hot tubs and costs £100-200 to retrofit. It won’t reduce chemicals as much as a CD ozone unit, but it helps.
Running Costs Breakdown
Real-world costs for a typical UK hot tub (1,200-1,500 litres, used 3-4 times per week):
Year 1 (Including Purchase and Installation)
- UV system — £400 upfront + £60 chemicals + £8 electricity = about £470 total
- Ozone (CD) — £350 upfront + £40 chemicals + £5 electricity = about £395 total
- Salt system — £600 upfront + £50 cells + £5 salt + £10 electricity = about £665 total
- No system (manual chlorine/bromine) — £0 upfront + £120 chemicals = about £120 total
Years 2-5 (Annual Ongoing)
- UV — £70 bulb + £60 chemicals + £8 electricity = about £138/year
- Ozone — £40 chemicals + £5 electricity = about £45/year (cell replacement in year 3-5 adds £150-250)
- Salt — £80-200 cells + £5 salt + £10 electricity = about £95-215/year
- Manual — £120 chemicals/year
The HSE guidance on Legionella prevention recommends maintaining proper sanitiser levels regardless of which system you use — these alternative systems supplement chemical treatment, they don’t replace it.
Installation and Retrofit
Factory-Fitted Systems
Many mid-range and premium hot tubs come with ozone or UV pre-installed. Brands that commonly include sanitiser systems:
- Jacuzzi — ClearRay UV on most models
- Hot Spring — FreshWater Salt System available on Highlife and Limelight ranges
- Sundance — UV-C system on most models
- Marquis — Ozone standard on mid-range and up
Retrofit Options
If your tub didn’t come with a system, retrofitting is usually possible but varies by complexity:
- Ozone — easiest retrofit. Most tubs have a pre-drilled ozone port in the plumbing. If yours does, installation takes under an hour. About £50-100 for a professional fitting on top of the unit cost.
- UV — requires plumbing modification. The UV chamber needs to be spliced into the filtration line, which means draining the tub, cutting pipe, and fitting unions. Professional installation recommended — about £100-200 for labour.
- Salt — most complex retrofit. The electrolytic cell needs a plumbing position with good flow, plus electrical connection to the control system. Some tub manufacturers void the warranty if you add salt. Always check before buying.
Combining Systems
Using two systems together is increasingly common and genuinely effective.
UV + Ozone
The gold standard combination. Ozone handles oxidisation (breaking down organic matter), UV handles pathogen kill. Together, they attack contamination from two different angles, and you can reduce your chemical residual to the bare minimum.
Cost: about £500-800 for both systems. Several manufacturers offer combination units.
Ozone + Salt
Less common but effective for people who want automated sanitation with powerful oxidisation. The ozone breaks down what the chlorine misses, and the salt system handles the residual automatically.
UV + Salt
Works well for maximum automation with clean water feel. The UV provides an extra layer of pathogen protection, and the salt system keeps chlorine levels consistent without manual dosing.
Maintenance Requirements
UV System Maintenance
- Monthly — check the UV indicator light is still on (if your system has one)
- Quarterly — remove and clean the quartz sleeve with a vinegar solution or specialist cleaner. Calcium buildup blocks UV light
- Annually — replace the UV bulb. Mark the date on your hot tub filter cleaning schedule so you don’t forget
Ozone System Maintenance
- Monthly — check the ozone indicator and sniff near the output (a faint fresh smell means it’s working)
- Annually — inspect the check valve. A failed check valve lets water back-flow into the ozone generator, destroying it
- Every 3-5 years — replace the CD cell or entire unit. Performance degrades gradually, so you might not notice the decline until water quality drops
Salt System Maintenance
- Weekly — check salt level with test strips (should read 2,000-3,000 ppm for most systems)
- Monthly — inspect the cell for calcium scale. Clean with a mild acid solution if needed
- Every 3-12 months — replace the electrolytic cell (varies hugely by model and usage)
Common Myths About Alternative Sanitisers
“I won’t need any chemicals at all”
False, and potentially dangerous. Every hot tub needs a measurable level of sanitiser in the water. UV and ozone kill pathogens during filtration, but the water is unprotected between cycles. Without residual sanitiser, bacteria can multiply rapidly in the warm water.
“Ozone damages hot tubs”
Partially true. Ozone can degrade certain rubber compounds — cheap headrests, pillow gaskets, and some O-rings are vulnerable. But quality hot tub components are ozone-rated. Check with your manufacturer, and if in doubt, stick with a system they recommend.
“Salt water is the same as the sea”
Not even close. A salt hot tub runs at about 2,000-3,000 ppm salt concentration. The sea is around 35,000 ppm — more than ten times saltier. You won’t taste the salt in your hot tub, and it won’t sting your eyes.
“UV systems use a lot of electricity”
A typical hot tub UV system uses 20-40 watts. Running it 12 hours a day costs roughly £8-10 per year at current UK electricity rates. Your hot tub heater uses 2,000-3,000 watts — the UV lamp is a rounding error on your energy bill.
According to Ofgem’s average energy usage data, a hot tub is already one of the higher electricity consumers in a household. Adding a UV or ozone system barely shifts the needle.
Frequently Asked Questions
Can I stop using chlorine if I install a UV system? No. UV kills pathogens as water passes through the chamber, but it leaves no residual protection in the water itself. You still need a small amount of chlorine or bromine (typically 1-2 ppm instead of the usual 3-5 ppm) to handle contamination between filtration cycles. Removing all chemical sanitiser risks dangerous bacterial growth, especially in warm hot tub water.
Which system requires the least maintenance? Ozone systems are the most hands-off. Once installed, a corona discharge ozone generator runs for 3-5 years with minimal attention — no bulbs to replace annually, no sleeves to clean quarterly. Salt systems are the most automated for daily sanitation but require regular cell inspection and replacement.
Will a salt system void my hot tub warranty? It depends on the manufacturer. Some brands (Hot Spring, Caldera) actively support salt systems. Others (particularly budget and mid-range brands) explicitly exclude salt damage from warranty coverage. Salt can corrode stainless steel components and certain plastics over time. Always check your warranty terms before installing a salt system.
Is ozone safe to breathe? In the tiny concentrations produced by hot tub ozone generators, it’s not a health concern. The ozone dissolves in water and reverts to oxygen within minutes. You might notice a faint fresh smell near the tub when the system is running, similar to the smell after a thunderstorm. If you can smell ozone strongly, the system may be overproducing or not mixing properly — have it checked.
How do I know if my existing ozone generator has stopped working? Three signs: increased chemical demand (you’re adding more chlorine than usual), water clarity declining faster, and the absence of the faint ozone smell near the tub. Many systems have an indicator light, but these can show green even when the ozone cell has degraded. Test strips showing consistently low oxidation reduction potential (ORP) are a more reliable indicator.