Saltwater pool chemistry: what's different and what to watch
A saltwater pool is a chlorine pool. Instead of adding chlorine from a bottle, a salt chlorine generator (SWG, or salt cell) makes it from salt dissolved in the water. That changes a few things about how you look after the water, mainly pH, stabilizer and the cell itself.
How a salt cell works
Pool water with a few thousand ppm of salt flows through the cell, where a low-voltage current passes between coated metal plates. This electrolysis turns chloride into chlorine, which dissolves as the same free chlorine you'd get from liquid chlorine. Once the chlorine has done its job, it turns back into chloride. That's why the salt isn't used up and only needs topping up when water is lost by splashing, backwashing or draining.
The cell's output is set as a percentage of the time it runs, or a production level, and it only makes chlorine while the pump runs water through it. Your daily chlorine depends on the cell's size, the output setting and how many hours the pump runs.
Levels for a saltwater pool
| Test | Typical saltwater target | Why it differs |
|---|---|---|
| Salt | Your generator's specified range, often around 3,200 ppm | The cell is designed for a specific range. Too low cuts output, too high can damage some cells. |
| Stabilizer (CYA) | Often 60–80 ppm (check the manual) | Higher CYA protects the chlorine the cell makes during the day, so the cell can run at a lower output. |
| Free chlorine | About 5% of CYA or more (e.g. 3–4 ppm at 70 ppm CYA) | The cell adds chlorine steadily, so the level dips less than with one daily dose. |
| pH | 7.4–7.6 (CDC range: 7.0–7.8) | pH tends to rise in salt pools, so expect to add acid regularly. |
| Total alkalinity | Around 60–80 ppm | Lower alkalinity slows the pH rise. |
| Calcium hardness | Per your surface, but watch for scale | The cell's plates are where scale tends to form first. |
The generator's manual is the authority for salt and often CYA. Makers differ: one major brand lists 2,700–3,400 ppm salt with 3,200 ppm as ideal, while others specify 3,000–3,500 ppm, 3,600 ppm, or more.
Adding salt
Use the pool salt calculator to find the amount. As a rule of thumb, raising 10,000 gallons by 100 ppm takes about 8.3 lb of salt. Use pool-grade sodium chloride without additives, turn the cell off while adding it, brush it around until it dissolves, and circulate for 24 hours before retesting. Since salt can only be lowered by replacing water, it's better to add a little less than the full dose and top up.
Why pH climbs, and what to do
Salt pools usually need acid more often than other chlorine pools. The cell's bubbling and the water features many salt pools have both drive carbon dioxide out of the water, and losing CO₂ raises pH. The most effective long-term fix is keeping total alkalinity lower, around 60–80 ppm. Some owners also add borates, which buffer pH. Use the pH calculator for acid doses and the pH and alkalinity guide for lowering alkalinity.
Looking after the cell
- Scale: white, crusty deposits on the plates reduce output. They form faster when pH, calcium or alkalinity is high, or the water is warm. Keeping the LSI near zero or slightly negative helps. Many cells reverse polarity to shed scale, but you may still need to inspect and clean the cell as the manual describes.
- Low salt warnings: test the salt yourself before adding any. The cell's reading can drift as it ages or in cold water.
- Cold water: many cells reduce or stop production below a set water temperature, often around 50–60 °F. Check yours. In cool weather you may need to add liquid chlorine.
- Lifespan: cells wear out after a few years of use. Running at a lower output for longer, with properly balanced water, is easier on the plates than running at full output.
Shocking a saltwater pool
Most cells have a "boost" or "superchlorinate" mode, but it raises chlorine slowly. For algae, add liquid chlorine to reach the shock level for your CYA, and keep the cell running. The shock calculator gives the dose. Avoid dichlor and trichlor, which add CYA.
Frequently asked questions
Is a saltwater pool chlorine-free?
No. It's sanitized by chlorine made in the cell, the same free chlorine as in any other chlorine pool. Many people find the water feels softer. A strong "chlorine" smell in any pool usually comes from combined chlorine (chloramines), and a cell that keeps free chlorine steady helps keep those low.
Is salt water bad for my pool equipment?
At around 3,000 ppm, pool water is roughly a tenth as salty as seawater, but it can still corrode some metals and soft natural stone over time, especially where water evaporates and leaves salt behind. Rinse coping and decking now and then, and check that heaters, ladders and lights are rated for saltwater use.
How long should the pump run for the cell?
Long enough for the cell to make the day's chlorine at its output setting. That's often longer in summer. If free chlorine keeps dropping, raise the output or run time before blaming the cell.