Free tool No. 5
How much salt to add
Test your salt, then add about 10 kg of pool salt per 10,000 litres for every 1,000 ppm you are below your target: the level in your salt chlorinator's manual, or 3,200 ppm if you don't have it. For example, a 50,000-litre pool that reads 2,400 ppm needs 40 kg to reach 3,200 ppm: 2 full 20-kg bags. Turn the chlorinator off, add the salt with the pump running, and turn the chlorinator back on after 24 hours.
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Worked example
A 50,000-litre salt pool reading 2,400 ppm, with pool salt in 20-kg bags.
- 1
Pick the target
Without the chlorinator's manual: aim for 3,200 ppm, inside 2,700 to 3,600 ppm
- 2
Work out the increase
3,200 ppm − 2,400 ppm = 800 ppm
- 3
Convert the volume
50,000 L ÷ 3.785 = 13,209 US gal
- 4
Dose the salt
SALT 2400 → 3200 ppm: 800 × 13,209 gal ÷ 7468.6 = 1414.8 oz
- 5
Convert to kilograms and round
1414.8 oz = 40.11 kg, rounded to 40 kg
- 6
Count the bags
40 kg ÷ 20 kg = 2 bags
Add 40 kg of pool salt (pure sodium chloride): 2 full 20-kg bags.
Turn the salt chlorinator off, pour the salt into the shallow end with the pump running, and brush it until it dissolves. Keep the pump running and the chlorinator off for 24 hours, then turn the chlorinator back on; its salt reading takes about that long to catch up. Add liquid chlorine in the meantime if chlorine drops.
Pool salt to reach 3,200 ppm
| Pool size | From 0 ppm | From 1,000 ppm | From 2,000 ppm | From 2,500 ppm | From 3,000 ppm |
|---|---|---|---|---|---|
| 20,000 L | 64 kg (3¼ bags) | 44 kg (2¼ bags) | 24 kg (1¼ bags) | 14 kg (¾ bag) | 4 kg (¼ bag) |
| 30,000 L | 96.5 kg (4¾ bags) | 66 kg (3¼ bags) | 36 kg (1¾ bags) | 21 kg (1 bag) | 6 kg (¼ bag) |
| 40,000 L | 130 kg (6½ bags) | 88 kg (4½ bags) | 48 kg (2½ bags) | 28 kg (1½ bags) | 8 kg (½ bag) |
| 50,000 L | 160 kg (8 bags) | 110 kg (5½ bags) | 60 kg (3 bags) | 35 kg (1¾ bags) | 10 kg (½ bag) |
| 60,000 L | 195 kg (9¾ bags) | 130 kg (6½ bags) | 72 kg (3½ bags) | 42 kg (2 bags) | 12 kg (½ bag) |
| 80,000 L | 255 kg (12¾ bags) | 175 kg (8¾ bags) | 96.5 kg (4¾ bags) | 56 kg (2¾ bags) | 16 kg (¾ bag) |
Amounts are rounded to what you can weigh, and bags to the nearest quarter. Retest 24 hours after adding salt, before you add more.
What your salt reading means
| Salt reading | What it means | What to do |
|---|---|---|
| Under 2,700 ppm | Low | Add salt to 3,200 ppm |
| 2,700 to 3,600 ppm | In range | Nothing, or top up to 3,200 ppm |
| Over 3,600, up to 4,000 ppm | Above the range | Add no more salt |
| Over 4,000 ppm | Too high | Replace some water, back to 3,200 ppm |
Low salt matters because the salt chlorinator makes less chlorine and may shut off. Salt only leaves the pool with water, so replacing some is the only way to lower it.
How to add salt to a pool
- 1
Test the salt level
Use a salt test kit or strips. The salt chlorinator's own reading lags: it takes about 24 hours to catch up after salt goes in.
- 2
Pick your target
Use the level in your salt chlorinator's manual, or 3,200 ppm if you don't have it. The calculator works out the amount for your pool and your bags.
- 3
Turn the salt chlorinator off
Leave it off while you add the salt and for 24 hours after, with the pump running.
- 4
Add the salt separately, with the pump running
Pour it into the shallow end and brush it around until it dissolves. If chlorine drops while the chlorinator is off, add liquid chlorine.
- 5
Retest after 24 hours
Test salt again, then turn the chlorinator back on. If salt is still short of your target, add the difference.
How we calculate
The amount in ounces is ppm to add × US gallons (your litres, converted) ÷ 7,468.64, because one ounce of salt raises 7,468.64 gallons by 1 ppm. That is about 10 kg of salt for every 1,000 ppm in 10,000 litres. The same chemistry engine as the app does the sum, then rounds it to what you can weigh and counts it in bags, to the nearest quarter.
What a reading means comes from the same engine. Without your salt chlorinator's range it aims for 3,200 ppm: below 2,700 ppm the app's plan adds salt, and above 4,000 ppm it replaces some water instead, the only way to lower salt. Set your own target and it aims for that, and replaces water only above 4,000 ppm or your target, whichever is higher.
Its limits: the amount is only as good as your salt reading, and the salt chlorinator's own reading lags about 24 hours after salt goes in. It assumes salt that is pure sodium chloride, and fill water with no salt in it when it works out a drain. It doesn't know your salt chlorinator's full range, so check the manual for the highest level it accepts. The drain advice assumes a plaster finish; for vinyl and fibreglass pools it is more cautious.
Questions
How many bags of salt does a new pool need?
From 0 to 3,200 ppm, the 50,000-litre example pool takes 160 kg of pool salt: 8 full 20-kg bags. Test the water first and add only the difference between your reading and your target.
How much does one bag of salt raise the level?
In the 50,000-litre example pool, one 20-kg bag raises salt by about 399 ppm. In a pool half that size, it raises it twice as much.
When can I turn the salt chlorinator back on?
After 24 hours. Keep the pump running and the chlorinator off while the salt dissolves. The chlorinator's own salt reading takes about that long to catch up, so check with a test kit before adding more. If chlorine drops in the meantime, add liquid chlorine.
What if I added too much salt?
Salt only comes down when you replace water. Up to 4,000 ppm, the app only stops adding salt; above that, it plans a partial drain back to your target. From 4,500 to 3,200 ppm, that means replacing about 29% of the water: 14,400 L in the example pool. Never drain the pool completely.
Does adding salt change my other readings?
No. Pool salt (pure sodium chloride) doesn't change chlorine, pH, alkalinity, calcium or stabiliser, so the calculator lists no side effects. The chlorinator itself pushes pH up as it runs, so keep testing pH.