A salt chlorinator is not a maintenance-free appliance — it is an electrochemical device with a limited service life. When free chlorine keeps falling after two or three seasons even at a 100 % setting, the vast majority of cases come down to one of three causes: a scaled-up cell, the wrong salinity, or simply worn-out plates at the end of their life. This guide shows you how to tell the causes apart and what to do about each of them.
If you are still deciding whether you want salt water at all, the comparison of both systems belongs in a separate article: salt water vs. chlorine. Here we are talking about running and maintaining equipment you already own.
How a salt chlorinator actually works and why it ages
A salt chlorinator does not produce “chlorine-free” water. Salt water flows through the electrolytic cell and a direct current breaks down the sodium chloride — the result is hypochlorite, the very same disinfectant you would pour from a canister. The difference is that it is produced continuously and right there in the pipework.
The key component is a set of titanium plates with a precious catalytic coating (typically ruthenium or iridium oxides). It is precisely that coating that is slowly consumed in operation — it is a wear part, much like brake pads. That is why manufacturers usually rate the cell in operating hours rather than in years.
Indicative service life: the figure commonly quoted is roughly 10,000 operating hours, which in domestic use works out at approximately 3–7 years, depending on how many hours a day the filtration runs and what condition the water is in. Always check the exact number in your unit’s manual — there are differences between brands and model ranges.
The second ageing mechanism is faster and, fortunately, reversible: scaling. During electrolysis the pH rises locally at the cathode and calcium carbonate precipitates out of the water directly onto the plates. The white coating acts as an insulator — the current has a smaller active area, chlorine output drops and the unit “tries” harder in the process, which puts it under needless strain.
Signs that something is wrong
A salt chlorinator rarely fails all at once. Typically it speaks up gradually, and in this order:
- Low free chlorine at full output. You set it to 100 %, the filtration runs its usual hours, and the test shows 0.3 mg/l instead of 0.8–1.0 mg/l. This is the most common first signal.
- A “low salt” warning even after adding salt. Most units have no real salt sensor — they estimate salinity from conductivity and from the current flowing through the cell. A scaled-up or worn cell conducts worse, the unit reads this as a lack of salt and reports an error, even though there is plenty of salt.
- A visible white coating on the plates. A flaky, chalky white deposit between the blades. On a transparent cell you can see it against the light, otherwise only after removal.
- Fluctuating or obviously nonsensical reported salinity. 2,400 ppm one moment, 3,600 ppm an hour later with nothing having changed.
- Cold water below 15 °C. This is often a false alarm — chlorine production naturally falls as the temperature drops and many units switch themselves off below a set threshold. It is not a fault.
Before you start dismantling the hardware, verify your measurements. Testing is covered in more detail in the article how to test pool and hot tub water — an old reagent or faded strips can “show” a problem that does not exist.
Cleaning the cell step by step
The procedure looks simple, but there is a reason for the order of the steps. Use acid as a last resort, not the first one — every acid clean takes away a little of the catalytic coating.
1. Start with a visual inspection
Switch off the filtration and the chlorinator, close the valves upstream and downstream of the cell and take the cell out. Look between the plates against the light. If the coating is minimal or absent, acid will fix nothing and the problem lies elsewhere (salinity, temperature, flow, age of the cell). Carry out a visual inspection at least twice a season.
2. The self-cleaning mode and its limits
Practically every modern salt chlorinator can reverse polarity: it periodically flips the direction of the current, which loosens the calcium deposit on the plates. It works well, but not perfectly — with hard water, a higher pH or short filtration runtimes the deposit builds up anyway. Reverse polarity is also not free of charge: frequent switching shortens the life of the plates, so there is no point in setting the shortest possible interval “just to be safe”.
3. Acid cleaning — with respect
Use only a weak acid intended for this purpose (commonly diluted hydrochloric acid or a dedicated cell-cleaning product). The rules that are not optional:
- Always add acid to water, never water to acid. The other way round leads to a violent reaction and splashing. Dilution of roughly 1 : 10 (one part acid into ten parts water).
- Goggles, acid-resistant gloves, an outdoor space with moving air.
- Stand the cell in a plastic container or use the original cleaning adapter so that the plates are submerged but the electrical connectors are not.
- Let it work for just a few minutes — until the fizzing clearly subsides. Typically 5–10 minutes, never “overnight”.
- Never use a wire brush, a scraper or any hard tool. A single mechanical scrape can destroy a coating that would otherwise have lasted for years.
- Rinse thoroughly with clean water and let it drain. Never pour leftover acid back into the pool; dispose of it according to local rules.
If you need acid more often than once or twice a season, you are not addressing the cause. And the cause is almost always a high pH or hard water.
The right salinity: how much salt and why it is not consumed
A salt chlorinator works within a narrow window. Most European units want roughly 3,000–4,000 ppm (that is 3–4 kg of salt per m³ of water), but there are models with both lower and higher requirements. The figure in the manual always takes precedence over a general recommendation.
What happens outside that range:
- Too little salt — the cell works under a higher load at a lower current, output falls and the life of the plates is shortened.
- Too much salt — a higher risk of corrosion of metal parts and, on some units, an error message. Over-salted water cannot be “de-salted” other than by partially replacing it.
One fundamental point many owners are not aware of: salt is not consumed. The chlorine created by electrolysis binds back into chloride once it has disinfected — it is a closed cycle. The concentration only falls through dilution (rain, topping up) and through the physical removal of water (backwashing the filter, splash-out, water carried away on bathers’ bodies). That is why you add salt more often in a rainy summer than in a dry one, and why it is worth knowing how much water you are actually losing — that is covered in pool water usage.
Always add salt gradually: dissolve it with the filtration running, ideally scattered across the floor away from the skimmer, and before you add another dose, wait several hours for the concentration to even out. Leave the chlorinator switched off until the salt has dissolved.
Water hardness and stabiliser: two parameters that decide the life of the cell
With salt water, two chemical parameters matter more than anywhere else.
Hardness and pH. The harder the water and the higher the pH, the faster the cell scales up. Salt water also has a natural tendency to push the pH upwards, so constantly topping up pH minus is a normal part of running the system. Keep the pH in the 7.0–7.4 band (rather towards the lower end) and keep an eye on calcium hardness — this is covered in detail in water hardness and scale build-up in the pool. With very hard water it pays either to top up with softened water or to plan for regular cell cleaning.
Stabiliser (cyanuric acid). A salt chlorinator produces chlorine in small doses and without CYA the sun would destroy it before it had a chance to work. That is why outdoor salt water pools usually keep a somewhat higher stabiliser level than a manually chlorinated pool. At the same time the familiar ceiling applies — too much CYA puts the chlorine “to sleep” and you then raise the unit’s output in vain. You will find the ranges and how to reduce stabiliser in the article chlorine stabiliser and cyanuric acid.
Winterising the salt chlorinator
The cell is one of the most expensive parts of pool technology, and frozen water inside it can destroy it in a single frosty night.
- Before the end of the season, remove the cell, clean it and let it dry completely.
- Store it somewhere dry and above freezing — ideally in its original box, not loose in the garage under your tools.
- Fit a winter bypass (dummy cell) into the pipework in place of the cell, if the manufacturer supplies one; otherwise drain the pipework properly.
- Disconnect the control unit from the power supply and protect it from moisture.
- The salt in the water does not go anywhere, so in spring you do not add salt “from zero” — you simply top it up to the measured value.
The full winter procedure for a pool, including chemistry and equipment, is described in winterising a pool step by step.
Corrosion around the pool: what salt water really does
A salinity of around 3,500 ppm is roughly one tenth the salinity of the sea — it is not an aggressive bath, but neither is it pure water. In the long run it shows up in three places:
- Stainless steel components. Ladders, handrails, railing anchors and jets made from cheaper steels (AISI 304) can suffer pitting corrosion around salt water. Salt water calls for AISI 316 stainless steel, ideally 316L.
- Natural stone and concrete coping. Salt wicks into the porous material, crystallises and flakes the surface off. Impregnation helps, and above all rinsing the coping thoroughly with clean water after the season.
- Anchors and fixings. The usual victims are ordinary galvanised bolts hidden under caps, where nobody ever looks. Check them once a year.
None of this is a reason not to have salt water — it is a reason to choose materials deliberately and not to cut corners on the anchoring parts.
Table: symptom → cause → solution
| Symptom | Probable cause | Solution |
|---|---|---|
| Low free chlorine at 100 % output | Scaled-up cell or high CYA | Visual inspection of the cell, acid cleaning if needed; measure the stabiliser |
| “Low salt” warning even after adding salt | Worn or fouled plates (lower conductivity) | Clean the cell; if the warning persists, the cell is at the end of its life |
| White flaky coating on the plates | High pH and hard water | Acid cleaning at 1 : 10 for a few minutes; then keep the pH at 7.0–7.4 |
| Output dropped after the water cooled | Low water temperature (below ~15 °C) | Normal behaviour; extend filtration or temporarily chlorinate by hand |
| Fluctuating salinity reading | Air in the pipework, low flow, dirty filter | Bleed the air, clean the filter, check the suction and the water level |
| Cell clean, salinity correct, chlorine still low | End of the plates’ service life | Replace the cell |
| Unit will not start, display dead | Power supply, fuse, control electronics | Check the breaker and the fuse; then call a service technician |
| Rust on the ladder or the anchors | Unsuitable grade of stainless steel | Replace with AISI 316, rinse and check the fixings |
Replace the cell, or the whole system?
The decision is usually straightforward if you ask yourself three questions.
Replace just the cell when the control unit works reliably, the display and its messages make sense, the unit is still in the manufacturer’s range and a matching cell is available. The cell is a consumable part and replacing it is a normal, planned investment after a few seasons.
Consider replacing the whole system when the unit is so old that a new cell can no longer be sourced, or the original cell is so expensive that its price approaches a whole new set-up. The same applies if your pool has grown (for example after a renovation) and the unit is undersized — a salt chlorinator should have some headroom for the water volume, not run permanently at maximum.
Always replace when the cell housing or the connectors are damaged. A leak under pressure and an electrical supply are not a combination worth patching up.
Frequently asked questions
How often should I check the cell?
Visually at least twice a season — after opening the pool and in midsummer. With hard water, preferably every month. Only carry out an acid clean when you can genuinely see a deposit, not preventively according to the calendar.
Can I use vinegar instead of acid for cleaning?
On a thin coating, vinegar or citric acid sometimes helps and is gentler on the plates. On heavy scaling, though, it is not very effective and you will have to leave it working for a long time, which cancels out the advantage. Products designed for cells have their formulation tuned for exactly this trade-off.
Why does my chlorinator report low salt when I have just added some?
Either the salt has not yet had time to dissolve and mix (wait 12–24 hours with the filtration running), or the unit is measuring conductivity through a fouled cell and the reading is misleading. The safest approach is to measure the salinity with an independent tester rather than relying on the display alone.
Do I still need other chemicals with salt water?
Yes. The chlorinator takes care of disinfection, but not of pH, hardness, alkalinity or flocculation. You will probably use more pH minus with salt water than with conventional chlorination. You will find an overview of routine maintenance in the pool maintenance calendar.
Does salt water shorten the life of the pump or the filtration?
At the correct salinity, not dramatically — modern pool equipment is built for salt water. Problems arise with over-salting and with older components made from unsuitable materials. Continuously monitored salinity and good-quality stainless steel are the whole of the prevention.
Summary: what to take away
A salt chlorinator rewards consistency. Keep the pH at the lower end of the band, the salinity within the range given in the manual, look through the cell against the light twice a year and use acid only when a deposit is genuinely visible — diluted 1 : 10, for a few minutes and never with a brush. If the cell is then clean, the salinity correct and the chlorine still low, there is nothing left to fine-tune: the plates have done their time and it is time for a new cell.
You will find replacement cells, measuring equipment and complete pool technology for salt water in the pool technology category, and chemicals for adjusting pH and hardness in the water treatment section. More practical guides are waiting in our Guide.
