Salt is the softener’s fuel and its only routine consumable, and the three types are not interchangeable in practice. Short version: pellets for most people, crystals if you check the tank regularly, potassium chloride only for the specific sodium reason.
The three types
| Type | What it is | Price (40 lb) | Best for |
|---|---|---|---|
| Evaporated pellets | Compressed, high-purity salt | $7–10 | Most households; fewest problems |
| Solar/rock crystals | Evaporated natural salt | $5–8 | Regular checkers in mild climates |
| Potassium chloride | KCl pellets, sodium-free exchange | $18–25 | Physician-directed sodium restriction |
Salt purity matters more than brand: look for 99%+ purity ratings, since insoluble residue becomes the sediment layer you dig out of brine tanks annually.
Bridging: the problem salt choice causes
A salt bridge is a hardened shelf of salt that forms above the water line, leaving an air gap; the system regenerates with plain water and hardness quietly returns. Push a broom handle into the tank; if it stops with resistance a few inches down, that is the bridge, and poking it through is the entire repair ($0). Pellets bridge least, dirty crystals bridge most, and half-empty tanks in humid garages bridge worst.
How much you will actually buy
At typical municipal hardness, a family of four consumes roughly 15–35 lb per month: one or two bags. Per year that is $40–120 in pellets, less for crystals, and roughly double for potassium chloride. The salt-dose setting moves this more than the type does; see the capacity explainer for the trade. Full annual math lives on the cost page.
Filling practice
Keep the tank between one-third and half full, never topped to the brim (deep salt columns bridge more). Buy one type and stay with it; mixing types is how bridges form. And store bags dry: salt that clumped in the garage is salt that will clump in the tank.
If the level stops dropping, that is a softener not using salt — almost always a bridge, not a fault. How fast the tank empties in the first place is set by regeneration frequency, which is itself set by how the unit was sized against your household demand.