How many bags of salt for a pool?
Salt math is the friendliest in pool care: it's pure NaCl, dosed by weight, and nothing consumes it. Starting a fresh fill from zero to 3,200 ppm:
| Pool volume | Salt needed | 40 lb bags |
|---|---|---|
| 10,000 gal | 267 lb | 7 |
| 15,000 gal | 401 lb | 10 |
| 20,000 gal | 534 lb | 14 |
| 25,000 gal | 668 lb | 17 |
Bags rounded up to whole bags. Top-ups are proportional: raising an existing 2,400 ppm to 3,200 takes a quarter of the startup amount.
Add it by broadcasting bags across the shallow end with the pump running and brushing until dissolved — usually a few hours. Keep the salt system off until the salt is fully dissolved and the level verified: cells measure conductivity where they sit, and a salt pile dissolving near the drain can read very differently from the pool at large. Wait 24 hours before trusting a reading.
Any NaCl labeled 99%+ pure with no additives: "pool salt" is the safe default, and plain water-softener crystals (not pellets with rust remover or anti-caking agents) are usually the same purity for less. Skip anything with yellow prussiate of soda (an anti-caking agent), iodized salt, and rock salt — the impurities can stain and the metals can wreck a liner. The bag should have one ingredient.
Salt too high? Water is the only way down
Like CYA and calcium, salt only leaves the pool inside water. Enter a target below your current reading above and you'll get the exact drain-and-refill percentage. Before you drain, though: verify high readings with an independent test (strips or a drop kit), because a failing cell's salt reading drifts — "salt too high" on the display with a normal test strip usually means a cell problem, not a salt problem. Most systems tolerate up to ~4,000 ppm without complaint; the water itself doesn't taste noticeably salty until around 5,000 (seawater is 35,000).
The cell converts salt to chlorine, the chlorine does its job and turns back into salt — a closed loop. Salt leaves only through splash-out, backwashing, overflow from heavy rain, and leaks. So if you're adding bags every month, something else is going on: most often a slow leak quietly replacing salty water with fresh fill. A stable salt reading is one of the best leak detectors you own.
A salt pool is a chlorine pool
The salt system doesn't replace chlorine — it manufactures it, on site, from the salt you added. That's genuinely great (no jugs to haul, steady dosing, soft-feeling water), but every rule of chlorine chemistry still applies: you still test FC, you still need CYA — more of it, in fact, 60–80 ppm, because SWG pools run best with extra sun protection — and the water still needs pH, alkalinity and calcium in range. The dashboard switches all its targets to SWG mode with one toggle.
One habit worth building: don't chase a low FC reading by adding more salt. Salt level and chlorine output are different knobs — if salt is in the window but FC is low, turn up the cell's output percentage or run the pump longer, and if that's maxed, the cell may be undersized or aging. Salt cell sizing has its own calculator for exactly that question.