Salt Pool Guide — How Much Salt to Add
Getting salinity right the first time, because the only way back down is draining water.
A saltwater pool is still a chlorine pool — the difference is where the chlorine comes from. A salt chlorine generator (SWG) passes dissolved salt over an electrolytic cell and converts it into chlorine continuously. That only works when salinity sits inside the window the cell was designed for, which is why the salt calculator treats your current and target ppm readings as the whole job.
How Salt Becomes Chlorine
The generator cell electrolyzes sodium chloride into chlorine gas, which dissolves instantly and sanitizes exactly like any other chlorine source. The salt itself is not consumed in the long run — after the chlorine does its work it largely reverts to salt, so salinity stays put unless water physically leaves the pool. Splash-out, filter backwashing, leaks, and heavy rain dilution are the real reasons levels drift, not evaporation, which leaves the salt behind.
The Math the Calculator Uses
The dose formula is: pounds of salt = (target ppm − current ppm) × (pool gallons ÷ 10,000) × 0.0834. That last factor means roughly 8.34 pounds of salt per 1,000 gallons raises salinity by 1,000 ppm — which makes sense, because a gallon of water weighs about 8.34 pounds and ppm is a ratio by weight. Worked example: a 15,000-gallon pool reading 2,600 ppm with a 3,200 ppm target needs a 600 ppm rise, so 600 × 1.5 × 0.0834 ≈ 75 pounds of salt.
Why the Target Defaults to 3,200 ppm
The calculator ships with a 3,200 ppm target and shows an ideal range of 2,700–3,400 ppm. The lower edge matters most: common residential generator cells specify at least 2,700 ppm, and below that threshold many units throttle output or stop producing chlorine entirely. Aiming for the middle of the band leaves a buffer, so normal dilution from rain or backwashing does not immediately drop the cell into a low-salt fault.
Adding Salt — and What to Do If You Overshoot
Broadcast salt across the shallow end with the pump running and let circulation dissolve it fully before retesting; high-purity evaporated pool salt dissolves cleanly, while rock salt or softener pellets can carry additives. Note that the calculator returns a dose only when your target is above your current reading. There is no chemical that removes salt — if you overshoot, the only correction is partially draining and refilling with fresh water, which is exactly why measuring the pool volume accurately before dosing pays off.
FAQ
How much salt does a 20,000-gallon pool need from a fresh fill?
Starting from 0 ppm with a 3,200 ppm target: 3,200 × (20,000 ÷ 10,000) × 0.0834 ≈ 534 pounds, or roughly thirteen to fourteen 40-pound bags. Always test first, though — fill water is rarely a true zero.
Does salt evaporate or wear out over the season?
No. Evaporating water leaves salt behind, and the generator's chemistry largely returns chlorine to salt after sanitizing. Salinity falls only when salty water leaves the pool — splash-out, backwashing, leaks — or when rain and fresh fill water dilute it.
Why does the calculator show no dose when my reading is above target?
Because there is nothing to add. The formula only computes additions; lowering salinity requires replacing part of the water with fresh water, so the tool deliberately stays silent instead of suggesting an impossible chemical fix.