How much salt for an 18,000 gallon pool

Starting with plain water, you'll pour roughly 480 lb of salt into an 18,000 gallon pool to hit 3,200 ppm (parts per million, the number a salt test shows). That works out to 12 bags at 40 lb each. Got some salt in the water already? Enter your reading and watch the bag count shrink.

Units Gallons, pounds Liters, kilograms

Pool volume in gallonsgal

Don't know the gallons? Measure the pool

Pool shapeRectangleOvalRoundKidney

A: lengthftB: widthftShallow end depthftDeep end depthft

The gallons above fill in as you measure.

Salt reading now ppmYour chlorinatorTarget to dose to ppm

Example For 18,000 gallons, from 0 to 3,200 ppm. Type yours to see your bags.

Buy 12 bags of

Add 480 lb in all: pour 11 bags now, then bag 12 after you retest.

Pump on. Pour it around the deep end, not into the skimmer.
Brush any salt off the floor until it's gone.
Run the pump 24 hours and test. Add the rest only if the reading is still short.

How this is worked out

Gallons = A × B × average depth × 7.5 for a rectangle, 6.7 for an oval and 5.9 for a round pool (diameter × diameter), the factors in Hayward's manual; 7.0 for a kidney (length × average width), from Inyo's sizing guide. Pounds of salt = (target ppm − your ppm) × gallons × 8.34 ÷ 1,000,000. A gallon of water weighs 8.34 pounds. Bags round up. In liters: kilograms = ppm difference × liters ÷ 1,000,000.

Salt for 18,000 gallons by current reading

Reading now	to 3,000 ppm	to 3,200 ppm	to 3,600 ppm
0 ppm	Buy 12 bagsadd 450 lb	Buy 12 bagsadd 480 lb	Buy 14 bagsadd 540 lb
1,000 ppm	Buy 8 bagsadd 300 lb	Buy 9 bagsadd 330 lb	Buy 10 bagsadd 390 lb
1,500 ppm	Buy 6 bagsadd 225 lb	Buy 7 bagsadd 255 lb	Buy 8 bagsadd 315 lb
2,000 ppm	Buy 4 bagsadd 150 lb	Buy 5 bagsadd 180 lb	Buy 6 bagsadd 240 lb
2,500 ppm	Buy 2 bagsadd 75 lb	Buy 3 bagsadd 105 lb	Buy 5 bagsadd 165 lb
2,800 ppm	Buy 1 bagadd 30 lb	Buy 2 bagsadd 60 lb	Buy 3 bagsadd 120 lb
3,000 ppm	Already there	Buy 1 bagadd 30 lb	Buy 3 bagsadd 90 lb

Every bag is 40 lb and the count rounds up. Pour all but the final bag, let the pump run a day, then test before you open it.

Intex and TruClear aim for 3,000 ppm, Hayward for 3,200 ppm and Pentair for 3,600 ppm. The chart by chlorinator lists every manufacturer's number.

Good to know at 18,000 gallons

In a pool this size, every 100 ppm gap takes 15.0 lb to close. So when your test reads 400 ppm under target, that's 60 lb: buy 2 bags of 40 lb.

CircuPool's advice is to buy a cell sized for 1.5 to 2 times the water you hold. For this pool that is 27,000 to 36,000 gallons, which fits the Pentair IntelliChlor LT25 or the Pentair IntelliChlor Plus30 or the Jandy TruClear.

Questions people bring to the counter

How much does a backwash or a rainy week cost me in salt?

Only the water you lose takes salt with it. If a top-up brings this pool from 2,800 back to 3,200 ppm, that's 60 lb: buy 2 bags of 40 lb.

How can I tell if my pool has enough salt?

Test the water. Most chlorinators light a low-salt warning below their range. A strip or drop kit reads in ppm, and that number goes in the salt reading box.

Next size down or up: 15,000 gal or 20,000 gal. Every size is on the per 1,000 gallons chart.