Quick Answer: For most metered softeners, evaporated pellet salt (Diamond Crystal Bright & Soft or Morton Clean & Protect) is the best buy — it’s roughly 99.9% pure, resists the mushing that clogs a brine tank, and runs about $8-$12 per 40-pound bag. Households on a sodium-restricted diet or a salt-sensitive septic system should use potassium chloride pellets instead, at roughly 2-3x the cost.
Not all water softener salt does the same job. The three common types — solar (evaporated seawater), rock (mined halite), and evaporated pellets — differ in purity, and impurities are what cause the buildup and bridging that stop a softener from regenerating properly. The Water Quality Association notes purity levels ranging from about 99.6% for solar salt up to 99.9%+ for evaporated pellet salt, with rock salt trailing both because it carries the most insoluble minerals. Buying the wrong salt is one of the most common reasons a correctly installed softener stops making soft water.
Water softener salt types at a glance
| Salt type | Best for | Purity | Price (40 lb) | Rating |
|---|---|---|---|---|
| Diamond Crystal Bright & Soft (pellet) | Best overall | ~99.9% | ~$10 | ★★★★★ |
| Morton Clean & Protect (pellet) | Widest availability | ~99.8% | ~$9 | ★★★★½ |
| Morton Potassium Chloride Pellets | Sodium-free / septic-safe | ~99% | ~$28 | ★★★★☆ |
| Cargill/Diamond Crystal Solar Salt (crystal) | Budget metered softeners | ~99.6% | ~$7 | ★★★★☆ |
| Generic rock salt (halite) | Cheapest, timer-based units | ~98.5% | ~$6 | ★★★☆☆ |
1. Diamond Crystal Bright & Soft — Best Overall
Diamond Crystal Bright & Soft Water Softener Pellets, 40 lb
- Extruded pellet shape dissolves evenly and resists forming the hard crust ("bridging") that leaves a softener running on empty brine.
- Very low insoluble content means less sludge to clean out of the brine tank at annual service time.
- Works in every metered and timer-based softener valve, including Fleck, Whirlpool, and GE systems.
Softener salt is heavy, and running out mid-week means hard water until the next bag arrives — Amazon Prime ships 40-pound bags free to your door in two days, and you can try it free for 30 days.
Pellet salt is the highest-purity option sold at consumer prices, and Diamond Crystal’s Bright & Soft is the pellet most plumbers stock their own homes with. The near-99.9% purity means almost nothing is left behind to cake against the tank walls, so you get more consistent regeneration cycles between top-offs and less maintenance. It costs a couple dollars more per bag than solar crystal, which is a rounding error against what a softener already saves you in appliance life.
2. Morton Clean & Protect — Widest Availability
Morton Clean & Protect Water Softener Pellets, 40 lb
- Rust-inhibiting formula helps protect pipes and fixtures on well water with trace iron.
- Sold at nearly every big-box and hardware store, so it's the easiest pellet salt to restock locally.
- Pellet form, so it shares pellet salt's low-bridging, low-residue advantages over crystal or rock.
Morton is the salt most people already recognize, and Clean & Protect is its pellet line built for softeners rather than the crystal Morton sells for ice melt. Performance is essentially tied with Diamond Crystal — pick this one if local pickup matters more than the last fraction of a percent of purity, or if your well water carries a trace of iron the rust-inhibitor formula is built to handle.
3. Morton Potassium Chloride Pellets — Sodium-Free / Septic-Safe
Morton Potassium Chloride Water Softener Pellets, 40 lb
- Regenerates the resin bed the same way sodium salt does, but adds potassium instead of sodium to your softened water.
- The choice for sodium-restricted diets and for septic systems in areas that regulate salt-brine discharge.
- Manufacturers typically recommend dosing 10% higher than sodium pellets since potassium ions are slightly less efficient at displacing hardness minerals.
Potassium chloride is the only softener salt that changes what’s actually added to your water, which is why it costs roughly 2-3x more than sodium pellets. It makes sense for two groups: people managing sodium intake for a medical reason, and homes on a septic system in a municipality that restricts chloride/sodium brine discharge. Everyone else gets no functional benefit from paying the premium — softened water already contains only a small amount of added sodium (roughly 7.5 mg per 8-oz glass per grain of hardness removed, well below a can of soda).
4. Cargill/Diamond Crystal Solar Salt — Budget Metered Pick
Diamond Crystal Solar Naturals Water Softener Crystals, 40 lb
- Naturally evaporated from seawater into coarse crystals — cheaper than pellets, still far cleaner than rock salt.
- Dissolves a bit more slowly than pellets, which is fine for a metered valve that regenerates on a weekly cycle.
- Good fit for budget-conscious households running one of the metered systems from our best water softener guide.
Solar salt splits the difference between rock salt’s rock-bottom price and pellet salt’s near-total purity. It’s the salt most softeners shipped with for decades and it still works fine in any metered system — the main downside next to pellets is a slightly higher chance of bridging in humid climates, so check the brine tank monthly for the first few months to learn your system’s habits.
How much salt does your softener actually need?
- Match salt dose to your resin’s regeneration setting, not a guess — check your valve’s manual (Fleck 5600SXT and 7000SXT both list salt dose per cubic foot of resin).
- Keep the brine tank at least a third full, but don’t overfill it — salt should sit above the water line, not be fully submerged, or it dissolves unevenly and wastes capacity.
- Break up any salt bridge you find (a hollow crust above the water) with a broom handle rather than letting the tank run dry, which stops regeneration entirely and lets hard water through untreated.
- Buy pellet or solar salt formulated for softeners — never table salt or ice-melt, which carry anti-caking agents and impurities that clog the resin bed and valve over years of use.
If you haven’t picked a softener yet, start with our best water softener roundup, or see best water softener for well water if you’re on a well with iron. For a no-salt alternative entirely, our water softener vs water conditioner guide breaks down what a salt-free conditioner can and can’t do.
The bottom line
For nearly every household, evaporated pellet salt — Diamond Crystal Bright & Soft or Morton Clean & Protect — is the right default: high purity, low maintenance, and only a few dollars more than crystal. Switch to potassium chloride only if you have a specific sodium or septic reason to, and skip rock salt unless you’re running an old timer-based unit and pinching every penny.