What salt level does your cell need?
A salt chlorine generator turns dissolved salt into chlorine, and it only works inside a set salt range. Hayward, for example, says its Aqua Rite cells run between 2,700 and 3,400 ppm and work best at about 3,200 ppm. Other brands sit in a similar band, but check the label on your cell or the manual before you buy salt.
Test with salt strips or a digital meter rather than relying only on the reading on the control box. Cells estimate salt from electrical conductivity, and the reading drifts as the cell ages or scales up.
The formula
Pounds of salt = gallons × 8.345 × (target − current ppm) ÷ 1,000,000 ÷ purity
Kilograms of salt = litres × (target − current ppm) ÷ 1,000,000 ÷ purity
One ppm is one milligram per litre. A US gallon of water weighs 8.345 lb, so 10,000 gallons needs 83.5 lb of pure salt for every 1,000 ppm rise.Worked example
15,000 gallons, reading 600 ppm, target 3,200 ppm
- Rise needed = 3,200 − 600 = 2,600 ppm
- Salt = 15,000 × 8.345 × 2,600 ÷ 1,000,000 = 325.5 lb of pure salt
- At 99% purity: 325.5 ÷ 0.99 = 329 lb, which is 8.2 bags of 40 lb
- Buy 9 bags, but add 7 or 8, let it dissolve, and test before adding the rest.
Going back up by small amounts is easy. Getting salt out means draining water, so it pays to creep up on the target.
Salt for a new or refilled pool
Starting from fresh fill water at about 0 ppm, here is what it takes to reach 3,200 ppm with 99% salt:
| Pool volume | Salt | 40 lb bags |
|---|---|---|
| 5,000 gal | 135 lb | 3.4 |
| 10,000 gal | 270 lb | 6.7 |
| 15,000 gal | 405 lb | 10.1 |
| 20,000 gal | 540 lb | 13.5 |
| 25,000 gal | 674 lb | 16.9 |
| 30,000 gal | 809 lb | 20.2 |
| 40,000 gal | 1,079 lb | 27 |
Salt needed to go from 0 to 3,200 ppm
How to add salt
- Turn the salt cell off. Leave the pump running.
- Use salt sold for pools, or plain sodium chloride of 99% or better with no additives. Skip rock salt, iodized salt and blends with anti-caking or rust-removal additives.
- Pour it into the shallow end or around the edges, away from the skimmer, so the cell doesn’t see a slug of very salty water.
- Brush the floor so piles dissolve and don’t sit on plaster.
- Run the pump for 24 hours, then test. Switch the cell back on once you’re in range.
If your cell shows a “low salt” warning but the strip test says you are in range, clean or inspect the cell before adding more. Scale on the plates makes the cell read low.
Why salt goes down, and what to do when it’s high
Salt doesn’t evaporate or burn off. You lose it when water leaves the pool as liquid: backwashing, splash-out, overflow after heavy rain, or draining. Topping up after evaporation adds water but no salt, so the level stays put. Over a season you might add a bag or two to make up for backwash and splash-out.
If you overshoot, the only fix is dilution. The drain and refill calculator shows how much water to swap out to get back to target.
Frequently asked questions
How many bags of salt do I need for a 10,000 gallon pool?
To go from 0 to 3,200 ppm you need about 270 lb, so 6.7 bags of 40 lb. Buy 7 bags, add 6 first and test.
How many bags of salt for a 20,000 gallon pool?
About 540 lb from fresh water to 3,200 ppm, which is 13.5 bags of 40 lb.
Can I use water softener salt?
Plain water softener pellets that are 99% or more sodium chloride with no additives are commonly used. Avoid products labeled for iron or rust removal, which contain additives you don’t want in a pool.
How long after adding salt can I swim?
Once it has dissolved. Brushing and running the pump usually clears it within a few hours, and the full reading settles within a day.
What happens if the salt level is too low?
The cell makes less chlorine or shuts down with a low-salt warning, and running a cell short of salt can shorten its life. Free chlorine then drifts down, which is when algae gets a start.
What happens if the salt level is too high?
Most cells show a high-salt warning and some stop producing. Very salty water can also taste noticeably salty. Drain and refill part of the pool to bring it down.
Does rain lower the salt level?
Only if the pool overflows or you lower the water afterwards. Rain adds fresh water, which dilutes slightly, but the salt stays until water leaves.
Sources
- How much salt does the system require?. Hayward (Aqua Rite salt chlorinators).
- NIST Guide to the SI, Appendix B: Conversion Factors. U.S. National Institute of Standards and Technology.
Reviewed November 7, 2026. We check the formulas against the sources above and re-run the worked examples whenever we update this page. Found something wrong? Tell us.