You’re shopping for a hot tub and the dealer mentions “salt water system” like it’s an upgrade worth paying for. Your mate has a chlorine tub and complains about red eyes and the chemical smell. The internet says salt water tubs are “chemical-free” and “better for your skin.” The internet, as usual, is about 60% right and 40% dangerously misleading.
Salt water hot tubs still use chlorine — they just make it from salt instead of adding it from a bottle. This distinction matters because it changes the maintenance routine, the running costs, the water feel, and what breaks when things go wrong. Here’s the honest comparison.
In This Article
- How Chlorine Hot Tubs Work
- How Salt Water Hot Tubs Work
- The Myth of Chemical-Free Salt Water
- Water Feel and Skin Effects
- Maintenance Comparison
- Running Costs
- Equipment and Installation
- Corrosion: The Hidden Salt Water Problem
- Water Chemistry Management
- Which Is Better for Sensitive Skin
- Converting a Chlorine Tub to Salt Water
- Which Should You Choose
- Frequently Asked Questions
How Chlorine Hot Tubs Work
Traditional chlorine hot tubs use manually added chlorine — either granules (sodium dichlor) or tablets — to sanitise the water. You test the water, add chlorine to maintain 3-5 ppm (parts per million) free chlorine, and the chlorine kills bacteria and algae on contact. You also need to shock the water weekly (a high dose of oxidiser to burn off combined chlorine and organic matter) and maintain pH between 7.2 and 7.6.
The Daily Routine
A well-maintained chlorine hot tub needs:
- Daily — test free chlorine and pH with test strips (30 seconds). Add chlorine granules if below 3 ppm
- Weekly — shock dose with non-chlorine shock or extra chlorine. Clean the waterline. Check alkalinity
- Monthly — deep clean filters. Check and adjust calcium hardness
- Every 3 months — drain and refill completely
What It Costs
Chlorine granules cost about £15-25 per kg, and a kg lasts most hot tub owners 2-3 months. Test strips cost about £8-12 for 100 (3-4 months). Non-chlorine shock is about £10-15 per tub. Total chemical cost: roughly £80-120 per year. Our hot tub chemicals guide breaks down the products you need.
How Salt Water Hot Tubs Work
Salt water systems use a device called a salt chlorine generator (or salt cell) that converts dissolved salt (sodium chloride) in the water into chlorine through electrolysis. You add about 1.5-3 kg of salt to the tub (much less than seawater — you can barely taste it), and the generator continuously produces chlorine from that salt, maintaining sanitiser levels automatically.
The Process
Salt water flows through the generator’s electrolytic cell. An electrical current splits the sodium chloride into sodium and chlorine. The chlorine sanitises the water, then recombines with the sodium to form salt again — a self-replenishing cycle. In theory, the salt never gets used up. In practice, you lose salt through splash-out, water replacement, and backwashing, so you need to top up occasionally.
What Makes It Different
The chlorine in a salt water tub is the same chemical (hypochlorous acid) as in a traditional chlorine tub. The difference is how it arrives:
- Traditional — you measure and add chlorine manually. Levels fluctuate between additions
- Salt water — the generator produces chlorine continuously at a low, steady rate. Levels stay more consistent
This consistency is the real advantage — not the absence of chlorine, but the steadiness of its presence.
The Myth of Chemical-Free Salt Water
Let’s be clear: salt water hot tubs are not chemical-free. They produce and use chlorine — the same sanitiser used in traditional tubs. The marketing claim of “no chemicals” or “natural sanitisation” is misleading.
What salt water systems DO reduce is the handling of chlorine products. You don’t open jars of granules, measure doses, or breathe in chlorine dust. The generator does the dosing automatically. This is a genuine convenience advantage, but it’s not the same as chemical-free.
What You Still Need
Even with a salt water system, you still need:
- pH adjusters — salt systems tend to push pH upward, requiring more pH-down than traditional chlorine systems
- Alkalinity adjusters — to buffer pH stability
- Calcium hardness management — critical for salt systems because the electrolysis process is affected by calcium levels
- Occasional shock treatment — the generator produces chlorine steadily but can’t handle heavy bather loads (a hot tub party) without supplemental shocking
- Test strips/kit — you still need to test water regularly
Water Feel and Skin Effects
This is where salt water has a genuine, noticeable advantage.
The Softness Factor
Salt water feels softer on the skin. The dissolved salt acts as a gentle exfoliant, and the consistent low-level chlorine (rather than the peaks and troughs of manual dosing) reduces the skin dryness and irritation that high chlorine spikes cause. Most people who’ve used both systems prefer the feel of salt water.
The Smell
Traditional chlorine tubs can develop a strong chemical smell — not from the chlorine itself, but from chloramines (combined chlorine) formed when free chlorine reacts with sweat, oils, and other organic matter. Salt water systems produce fewer chloramines because the continuous low-level chlorine burns off organic matter before it accumulates. Less chloramine means less chemical smell and fewer red, irritated eyes.
Hair and Swimwear
Salt water is gentler on hair and swimwear than traditional chlorine at the same concentration. The steady, low-level dosing causes less bleaching and degradation than the higher peak concentrations typical of manual dosing. Blonde hair in particular stays less green in salt water tubs.
Maintenance Comparison
Salt Water: Less Frequent, Different Tasks
Salt water tubs need less daily attention because the generator maintains chlorine levels automatically. However, they introduce new maintenance tasks:
- Cell cleaning — the electrolytic cell builds up calcium scale every 1-3 months. You need to clean it with a mild acid wash (white vinegar or diluted muriatic acid). A neglected cell stops producing chlorine
- Cell replacement — salt cells last 2-5 years depending on usage, then need replacing. Cost: £150-400 depending on the system
- pH management — salt systems push pH up consistently. You’ll use more pH-down than with traditional chlorine
- Salt level testing — check every 2-4 weeks with a salt test strip
Traditional Chlorine: More Frequent, Simpler
Chlorine tubs need more daily attention (testing and dosing) but the maintenance is simpler and uses cheaper, widely available products. There’s no specialist equipment to maintain or replace. If something goes wrong, the fix is usually “add more chlorine” or “shock the water.”
The Honest Verdict
Salt water reduces daily hands-on time by 2-3 minutes. But it adds periodic tasks (cell cleaning, cell replacement) that are more complex and expensive than anything a traditional chlorine tub requires. If you’re diligent about daily testing, traditional chlorine is simpler overall. If you hate daily chemical handling, salt water automates the most annoying part.
Running Costs
Traditional Chlorine: About £80-120 Per Year
Chlorine granules, test strips, pH adjusters, non-chlorine shock, and filter cleaner. All products are cheap, widely available (Amazon, hot tub dealers, even Screwfix), and have long shelf lives.
Salt Water: About £60-100 Per Year in Chemicals, Plus Cell Replacement
The salt itself is cheap (about £5-10 per year). You’ll use fewer chlorine products but more pH-down. The hidden cost is cell replacement: a new salt cell every 2-5 years at £150-400. Amortised over 5 years, this adds £30-80 per year to running costs.
Total Cost of Ownership (5 Years)
- Traditional chlorine — about £400-600 in chemicals over 5 years
- Salt water — about £300-500 in chemicals plus £150-400 for one cell replacement = £450-900 over 5 years
Salt water costs more in total, primarily because of the cell replacement. The daily chemical savings don’t offset the equipment cost for most owners.
Equipment and Installation
Adding Salt Water to a New Hot Tub
Some hot tubs come with salt water systems factory-installed (Jacuzzi, Hot Spring, and some Artesian models). These are integrated into the plumbing and electrical system and work seamlessly. Expect to pay £500-1,500 more for a salt-water-ready tub compared to the same model without.
Retrofitting Salt Water to an Existing Tub
Aftermarket salt chlorine generators (about £300-600) can be added to most existing hot tubs. Installation involves plumbing the cell into the circulation loop and wiring it to a power source. Some require professional installation; others are designed for DIY fitting. Check your tub manufacturer’s warranty before retrofitting — some void the warranty if unapproved equipment is added to the plumbing.
Corrosion: The Hidden Salt Water Problem
Salt corrodes metal. This is the biggest long-term concern with salt water hot tubs.
What Gets Damaged
- Metal fittings — stainless steel jet faces, screws, and fasteners can corrode faster in salt water. Most quality hot tubs use 316-grade stainless steel (marine grade) which resists salt, but cheaper tubs use 304-grade which doesn’t
- Heater elements — salt can accelerate scaling and corrosion on the heater, reducing efficiency and lifespan
- Equipment pads and covers — salt residue from splash-out corrodes nearby metal surfaces, concrete pads, and cover hardware
- The salt cell itself — the electrodes degrade over time as they’re consumed by the electrolysis process
Mitigation
Rinse the area around the tub regularly to prevent salt buildup. Check metal fittings quarterly for signs of corrosion. Use sacrificial zinc anodes (about £10-15, available from hot tub dealers) — they corrode preferentially, protecting the tub’s metal components. Ensure your tub uses marine-grade stainless steel if running salt water.
Water Chemistry Management
Traditional Chlorine Chemistry
Relatively forgiving. Test and adjust free chlorine, pH, and alkalinity. The chemistry is well understood, products are widely available, and problems have simple fixes. Over-chlorinate? Run the jets with the cover off for an hour. pH too high? Add pH-down. The NHS guidance on water-borne bacteria underscores why maintaining proper sanitiser levels is critical regardless of which system you use.
Salt Water Chemistry
More complex because you’re managing additional variables — salt concentration, cell output level, and the pH drift caused by electrolysis. The generator only works correctly within a narrow salt concentration window (typically 2,000-3,000 ppm). Too little salt and it can’t produce enough chlorine. Too much and it damages the cell. You need a salt-specific test kit alongside your regular water chemistry tests.
pH Drift: The Salt Water Headache
Electrolysis produces sodium hydroxide as a byproduct, which raises pH. Salt water tubs typically drift upward to pH 7.8-8.0 between adjustments, while chlorine tubs stay more stable. High pH reduces chlorine effectiveness and causes scale formation. You’ll add pH-down more frequently with a salt system — often 2-3 times per week versus once a week with traditional chlorine.
Which Is Better for Sensitive Skin
Salt Water Advantages
The consistent, low-level chlorine exposure causes less skin irritation than the peaks of manual dosing. The dissolved salt has a mild moisturising effect. Fewer chloramines mean fewer eye and respiratory irritations. For people with mild skin sensitivity, salt water is noticeably more comfortable.
When It Doesn’t Help
If you’re allergic to chlorine specifically (rare but real), salt water doesn’t help — it still produces chlorine. For chlorine allergies, bromine-based sanitation is the alternative. For eczema and psoriasis, any hot tub use requires caution regardless of sanitiser type — the combination of hot water, chemicals, and prolonged soaking can trigger flare-ups.
The Pragmatic Alternative
If you want softer water without the complexity of a salt system, use a mineral sanitiser (like Silk Balance or Nature2) alongside reduced chlorine dosing. This gives you the softer water feel with simpler maintenance than salt.
Converting a Chlorine Tub to Salt Water
Is It Worth It?
If your current tub is modern (less than 5 years old) and has marine-grade stainless fittings, conversion is feasible. The aftermarket generator costs £300-600 plus installation. If your tub is older or has standard stainless steel fittings, the corrosion risk makes conversion questionable — the salt could shorten the tub’s remaining lifespan.
The Process
- Purchase a compatible aftermarket salt chlorine generator
- Plumb the cell into the circulation loop (after the heater, before the return jets)
- Wire the controller to a power source
- Add the recommended amount of salt (typically 2-3 kg for a standard hot tub)
- Drain and refill with fresh water first — don’t add salt to old water with accumulated chemicals
- Run the system for 24 hours, test chlorine output, and adjust the generator’s production level
What to Check Before Converting
- Warranty — will the manufacturer void your warranty? Most will if you modify the plumbing
- Metal grade — check jet faces, screws, and heater housing for 316 stainless steel markings
- Space — the cell and controller need physical space in the equipment bay
- Existing equipment compatibility — some circulation pumps and heaters aren’t rated for salt water use
Which Should You Choose
Choose Salt Water If:
- You hate handling chemicals and want automated sanitisation
- You have sensitive skin or eyes that react to chloramine
- You’re buying a new tub with a factory-installed salt system (avoiding retrofit risks)
- You’re willing to manage the extra complexity of salt chemistry and cell maintenance
- Budget for cell replacement every 2-5 years isn’t a concern
Choose Traditional Chlorine If:
- You want the simplest, cheapest maintenance routine
- You’re comfortable with daily testing and dosing (it takes 2-3 minutes)
- Your tub doesn’t have marine-grade stainless steel fittings
- You want widely available, cheap products from any supplier
- You prefer lower total cost of ownership over 5+ years
The Verdict for Most UK Hot Tub Owners
Traditional chlorine. It’s simpler, cheaper over time, and the products are available everywhere from Amazon to Screwfix. The daily maintenance takes 2-3 minutes and becomes second nature within a week. Salt water is a genuine luxury upgrade for people who value softer water and automated dosing — but it’s not the revolution the marketing suggests.
Frequently Asked Questions
Do salt water hot tubs still use chlorine? Yes. Salt water systems produce chlorine from dissolved salt through electrolysis. The chlorine is identical to what you add from a bottle in a traditional system. The difference is that the generator produces it automatically at a steady rate rather than you adding it manually.
Is a salt water hot tub better for your skin? For most people, yes. The consistent low-level chlorine causes less irritation than the peaks and troughs of manual dosing. The dissolved salt has a mild softening effect. Fewer chloramines mean less chemical smell and fewer red eyes. However, if you have a true chlorine allergy, salt water doesn’t help — it still produces chlorine.
How much does a salt water system cost? Factory-installed systems add £500-1,500 to the tub price. Aftermarket retrofit generators cost £300-600 plus installation. Replacement salt cells cost £150-400 every 2-5 years. Over 5 years, total ownership cost is typically higher than traditional chlorine.
Can I convert my existing hot tub to salt water? Usually, if the tub is modern and has marine-grade stainless steel fittings. Aftermarket generators plumb into the circulation loop. Check your warranty first — most manufacturers void coverage if the plumbing is modified. The conversion costs £300-600 for the equipment.
Which is easier to maintain, salt water or chlorine? Chlorine requires more frequent attention (daily testing and dosing) but the tasks are simpler. Salt water requires less daily input but introduces more complex periodic maintenance (cell cleaning, salt testing, managing pH drift). Overall, chlorine is simpler for most people.