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RecommendedHow Much Salt a Pool Needs
A salt chlorine generator does not remove the need for chlorine. It makes chlorine on site by electrolysing dissolved salt as water passes through the cell. For that to work, the salinity has to sit in the band the cell was designed for, and for most residential generators that band is 3,000 to 3,500 ppm. Below it, the cell underproduces and many units throw a low salt fault. Above it, output does not improve and corrosion risk on metal fittings rises.
Salt requiredPounds of salt = (target ppm - current ppm) x gallons x 0.0000083
That constant works out to roughly 8.35 lb of salt per 1,000 gallons to raise salinity by 1,000 ppm.
Worked example
A 20,000 gallon pool tests at 2,400 ppm and the generator wants 3,200 ppm. The gap is 800 ppm. Pounds equal 800 x 20,000 x 0.0000083, which is 132.8 lb. That is three 40 lb bags plus a little, so three bags is the sensible order, followed by a retest.
The same pool starting from a fresh fill at 0 ppm needs 3,200 x 20,000 x 0.0000083, which is 531 lb, or roughly fourteen 40 lb bags.
Never dose blindAlways test current salinity before adding salt. Starting from an assumed reading rather than a measured one is the most common cause of an overshoot, and an overshoot can only be corrected by draining water out.
Salt Does Not Evaporate
This is the fact that changes how a saltwater pool is managed. Water evaporates. Salt stays behind. Topping up an evaporating pool with fresh water returns the level, and the salinity goes back to where it was, because the salt never left.
Salt leaves a pool only three ways:
- Splash-out. Water carried out of the pool by swimmers, waves and overflow takes dissolved salt with it.
- Backwashing and filter cleaning. Every backwash sends salted water to waste and is replaced with fresh water.
- Dilution. Heavy rain, an overflowing pool, a partial drain, or a leak, all of which replace salted water with unsalted water.
Because of this, a properly salted pool usually needs only a modest top-up once or twice a season, mostly after backwashing or a wet spell. A pool that seems to need salt constantly is losing water somewhere, and the leak is the real problem.
Fresh Fill Salt Requirements
These figures are for taking a pool from zero salinity to 3,200 ppm, which sits comfortably inside the usual 3,000 to 3,500 ppm window. Bags are 40 lb, rounded up.
Pool volumeSalt to reach 3,200 ppm40 lb bags
10,000 gallons267 lb7
15,000 gallons401 lb10
20,000 gallons534 lb14
25,000 gallons668 lb17
30,000 gallons802 lb20
Use the Right Salt
Buy pool grade salt, sold as at least 99.8 percent pure sodium chloride, evaporated and free of additives. It dissolves cleanly and leaves nothing behind.
- Avoid iodised table salt. The additives can discolour water.
- Avoid rock salt and de-icing salt. These carry insoluble grit and often iron and other minerals that stain plaster and vinyl.
- Avoid anti-caking treated water softener salt. Untreated solar or evaporated softener salt at 99.8 percent purity is acceptable, but read the bag, because many softener salts include additives.
Adding Salt Correctly
Run the circulation pump throughout and for at least 24 hours afterwards. Turn the salt chlorine generator off while the salt dissolves, so the cell does not run in water it cannot read properly.
- Test current salinity with a meter or test strips, and note the reading.
- Calculate the requirement from the gap, not from the target.
- Broadcast the salt across the deep end with the pump running. Do not pour it into the skimmer, which sends undissolved salt through the pump and cell.
- Brush the pool floor to break up piles and speed dissolution. Undissolved salt sitting on plaster can etch it.
- Wait 24 hours with the pump running, then retest before adding any more.
- Turn the generator back on once the reading is stable and inside range.
Wait a full 24 hours before retestingSalt takes hours to distribute evenly. Testing too early gives a low reading, which tempts a second dose that the pool does not need.
What Happens If You Overshoot
There is no chemical that removes salt from pool water. The only way down is dilution: drain a measured volume and refill with fresh water. To drop salinity by a given fraction, drain and replace roughly that same fraction of the pool volume.
For example, a 20,000 gallon pool at 4,200 ppm that needs to reach 3,200 ppm has to lose about 24 percent of its salt, so drain and refill roughly 4,800 gallons. That also dilutes stabiliser, calcium hardness and alkalinity, all of which then need retesting and correcting. This is why conservative dosing matters: add about 80 percent of the calculated amount, retest, and top up.
Salinity and the Rest of the Water
Salt is not a substitute for balanced water. A salt pool still needs pH in the 7.4 to 7.6 range, total alkalinity in the 80 to 120 ppm range, calcium hardness in the 200 to 400 ppm range and cyanuric acid in the 30 to 50 ppm range. Salt generators tend to push pH upward over time, so acid demand is normal on a salt pool and should be planned for rather than treated as a fault.
Cell life also depends on scale control. Water that runs high in pH and calcium will scale the cell plates, cutting output, which then reads as a salt problem when it is actually a scaling problem. Inspect and clean the cell on the schedule the manufacturer specifies before assuming more salt is the answer.