Most salt chlorinators want somewhere around 3,000 to 3,500 ppm, and the arithmetic is simple once you know your pool volume: every 1,000 ppm you need to add takes about 8.3 lb of salt per 1,000 gallons, or 1 kg per 1,000 litres. The part that catches people out is not the maths — it is that salt only leaves a pool in water, so it is far easier to add too much than to take any out.
Water Health Check
Enter your test results and see what is in range, what is not, and what to do first.
CalculateWhat level you are aiming for
Check the manual for your chlorinator before anything else, because the ideal figure is set by the cell, not by the water. Most fall in a narrow band.
| Level | ppm | What happens |
|---|---|---|
| Too low | Below 2,700 | Cell stops producing; most units show a warning |
| Typical target | 3,000–3,500 | Normal running range |
| Too high | Above 4,500 | Corrosion risk on metal fittings and ladders |
| Noticeably salty | Above 3,500 | You start to taste it |
For comparison, seawater is around 35,000 ppm. A salt pool is about a tenth of that, which is why it does not taste like the sea and why it does not sting your eyes the way people expect.
The arithmetic
Salt is measured in parts per million, which is a weight ratio, so the sum is the same in any unit system once you line the units up.
US: pounds of salt = gallons × ppm increase × 0.00000834
Metric: kilograms of salt = litres × ppm increase ÷ 1,000,000
A worked example in each. A 20,000 gallon pool reading 2,600 ppm, aiming for 3,200, needs a 600 ppm increase: 20,000 × 600 × 0.00000834 = 100 lb, which is two and a half 40 lb bags.
A 50,000 litre pool in the same position needs 50,000 × 600 ÷ 1,000,000 = 30 kg, which is one and a half 20 kg bags.
Starting from empty
A pool filled with fresh water is not quite at zero — tap water usually carries 100 to 400 ppm already — but it is close enough that you are adding the full target.
| Pool size | Salt for 3,200 ppm | Bags |
|---|---|---|
| 10,000 gal (38,000 L) | 267 lb / 121 kg | 7 × 40 lb |
| 15,000 gal (57,000 L) | 400 lb / 182 kg | 10 × 40 lb |
| 20,000 gal (76,000 L) | 534 lb / 242 kg | 14 × 40 lb |
| 30,000 gal (114,000 L) | 800 lb / 363 kg | 20 × 40 lb |
| 50,000 litres | 160 kg | 8 × 20 kg |
Those figures assume you are starting from fresh water. If the pool already has some salt in it, test first and add only the difference — this is the single most common way people overshoot.
Which salt to buy
You want sodium chloride at 99.8% purity or better, sold as pool salt or water softener salt. What matters is what is not in it: avoid rock salt, which carries dirt and minerals that stain, and avoid anything with an anti-caking agent such as yellow prussiate of soda, which can stain too.
Iodised table salt is a poor choice at this scale, and salt sold for de-icing roads is the worst of the options. Fine-grain pool salt dissolves faster than crystals, which is worth the small extra cost when you are adding hundreds of pounds.
How to add it
- Test first. Use a salt test strip or a meter, or take a sample to a pool shop. Do not work from what the chlorinator display says — cells drift as they age and the reading is often the thing that is wrong.
- Turn the chlorinator off, leave the pump running on a normal cycle.
- Pour it into the shallow end, spread along the floor. Never down the skimmer — a slug of concentrated brine going through the pump and cell is how cells get damaged.
- Brush it around to stop it sitting in a pile on the floor, especially on a vinyl liner.
- Wait 24 hours with the pump running before you test again or switch the chlorinator back on.
- Add in stages if you need a lot. Three quarters now, test, then the rest.
There is no way to remove salt except by removing water. If you overshoot, the only fix is to drain part of the pool and refill with fresh water — which also means losing the chemicals in it and rebalancing afterwards. Erring low costs you one more trip to the shop; erring high costs you a day.
Why the level drops
Salt does not evaporate and the chlorinator does not consume it — the cell splits it into chlorine and the chlorine eventually turns back into salt. So a closed pool holds its level almost indefinitely.
It falls when water leaves: backwashing the filter, splash-out, heavy rain overflowing the pool, draining to lower the level, and leaks. Topping up for evaporation does not dilute it, because evaporation takes the water and leaves the salt behind.
Most pools need a top-up once or twice a season, usually after opening and after a wet spell.
Common questions
How many bags of salt for a 50,000 litre pool?
From fresh water to 3,200 ppm, about 160 kg — eight 20 kg bags. If the pool already reads 2,600 ppm you need only the 600 ppm difference, which is 30 kg, so one and a half bags. Always test before buying; the gap between those two answers is six bags.
Can I add salt and swim the same day?
Yes. Salt is not a sanitiser and it is not harmful at these levels, so swimming while it dissolves is fine. The one thing to avoid is swimming over an undissolved pile on the floor, which is abrasive underfoot. Brush it out and it is a non-issue.
My chlorinator says low salt but my test says fine
Trust the test. Cells measure salt indirectly through conductivity, and both cold water and a scaled or ageing cell read low. If your water is under about 60°F the reading will drop even though nothing changed. Clean the cell, retest the water properly, and only add salt if the water sample agrees.
Does a salt pool still need chlorine?
It makes its own, which is the point — but it is still a chlorine pool, and it still needs its free chlorine, pH, alkalinity and stabiliser in range. A salt pool with no stabiliser loses chlorine to sunlight as fast as any other. See saltwater against traditional chlorine for what actually differs.