Salt treatment: how it really works
This is the most widespread misunderstanding in pool maintenance. A salt pool is a chlorine pool — the chlorine is simply made on site instead of being delivered in drums. And that changes a lot of things day to day.
The principle
Salt is dissolved in the pool water, at 3 to 5 grams per litre depending on the unit. For comparison, sea water contains about 35: we are a long way from a salt bath, and that is why you can barely taste it.
The salt water then passes through an electrolysis cell fitted on the filtration circuit. A low-voltage electric current breaks down the salt there and produces active chlorine, which disinfects the pool. Once its work is done, that chlorine recombines into salt. The cycle closes: you hardly ever top up, apart from losses through splashing, filter backwashes and water renewal.
The real advantages
- No more chlorine drums to buy, carry and store.
- Continuous, steady production, instead of surges after each manual addition.
- Water that is markedly gentler on skin and eyes, with no chlorine smell — as long as the balance is held: it is the imbalance that creates the smell, not the chlorine itself.
- Fewer purchases of treatment products over the season, against the cost of the unit and of replacing its cell.
The five points to watch
1. The minimum flow rate
This is the point least often explained at the point of sale. A salt chlorinator needs a minimum water flow rate to work: it depends on the cell installed and is given in its manual. If you have a variable-speed pump set too low, the unit stops producing — often with no clear warning. Both settings must be made together: see a correctly calculated filtration time.
2. The pH that rises on its own
Electrolysis naturally pushes the pH up. Without correction it drifts upwards, the chlorine loses effectiveness and limescale builds up. An automatic pH controller is not a luxury on a salt installation: it is almost an essential complement.
3. The water balance
Electrolysis does not remove the need to watch the basic parameters. The usual reference points: pH between 7.0 and 7.4, free chlorine between 0.5 and 2 mg/L, total alkalinity between 80 and 150 mg/L, and hardness around 15 °f, without exceeding 25 to 30. Alkalinity that is too low makes the pH unstable and impossible to hold.
4. Scaling of the cell
The electrodes scale up, particularly with hard water of the kind often found here. Most units automatically reverse the polarity to lift the deposit, but a visual check at the end of the season is still necessary. A scaled cell produces less, heats up more and wears out faster.
5. Salt and metal
Salt water is more corrosive to certain metals. Ladders, lights, built-in fittings and coping must be compatible. On a new installation, this is chosen from the outset; on an older pool converted to salt, it is checked before conversion.
And in winter?
Below about 15 °C, most salt chlorinators produce poorly and wear out needlessly. In a mild climate where the pool is not fully winterised, you lower the output or switch the unit off and use a supplementary treatment over that period.
Salt, flow rate, pH, hardness: these four settings hold each other up, and that is why a salt chlorinator fitted on its own so often disappoints. Before equipping an existing pool, have the water and the real flow rate checked: it is one visit, not a building project.