Water softener salt types compared: pellets vs crystals vs solar vs block

Buy evaporated salt pellets or coarse solar salt crystals. Pellets are the purest and leave the least sludge in the brine tank, the shorter tank that holds the salt. Solar crystals often cost a little less and work fine if you clean that tank on schedule.

Skip rock salt, table salt and ice-cream salt, and only buy block salt if your softener's manual asks for it. Two other bags have a place: pellets with an iron additive for water with a little clear-water iron, and potassium chloride for homes avoiding added sodium.

The aisle doesn't make this easy. You're facing bags labeled pellets, crystals, iron fighter and potassium, next to a cheap pallet of ice melt. Every one of them promises softer water.

Which salt to buy: every bag on the shelf, compared

To narrow it to one bag, match your house to the first line that fits:

• An all-in-one cabinet softener: pellets. In these units the brine tank is the cabinet itself, wrapped around the resin tank (the tall tank that does the softening). Its floor is awkward to clean, so the purest salt pays off most.
• Well water with a little clear-water iron (water that comes out clear and turns orange after it sits): pellets with an iron additive. Past about 1 to 3 ppm of iron, depending on the unit, a softener can't keep up and the water needs a dedicated iron filter.
• A standard softener with a separate brine tank, on city water: pellets or solar crystals, whichever costs less where you shop.
• A household avoiding added sodium: potassium chloride.

Why purity matters more than the brand

Everything in the bag that isn't salt stays behind. Each regeneration, the softener's cleaning cycle, dissolves salt into the water at the bottom of the brine tank and pulls that brine away. Clay, sand and other insoluble bits can't dissolve, so they settle and pile up. Salt producer Cargill describes exactly this buildup on the floor of the brine tank.

You can run the math for your own house. A typical home uses about 40 to 80 pounds of salt a month, roughly 480 to 960 pounds a year. Every 1% of insoluble material in that salt leaves about 5 to 10 pounds of grit in the tank each year. A bag sold as 99.5% pure has at most half a percent of other material, so at most about 2.5 to 5 pounds a year.

That grit feeds a layer of salt mush at the bottom of the tank. Some of it travels up the brine line, the small tube that carries brine to the control valve on top of the resin tank. There it can lodge in the injector, the tiny nozzle in the valve that draws the brine in.

Humidity causes the other classic problem. Damp, clumping salt can fuse into a salt bridge, a hard crust that hangs over empty space while the water below stays weak. GE Appliances names the wrong salt and high humidity as the most common causes. Push a broom handle down through the salt, and if it stops on a hard crust partway down, that's a bridge.

Evaporated pellets: the default for most homes

Evaporated salt starts as brine that's purified and boiled down, then pressed into uniform pellets. It's the purest salt sold for softeners, so it leaves the least residue. The even shape also lets water move freely around the bottom of the pile.

Pellets are the safe pick when you'd rather not think about salt at all, and they suit every standard softener. Once you've chosen a bag, how much salt your softener uses tells you how often you'll be buying it.

Solar salt crystals: cheaper and nearly as clean

Solar salt is made by letting seawater or natural brine evaporate in outdoor ponds. Cargill puts its purity typically above 99.5% sodium chloride, which meets what softener manuals ask for. It often sells at the cheaper end of the shelf.

The trade-off is that last fraction of a percent. Over a few years it shows up as a thin layer of sand and silt at the bottom of the tank. Cleaning the brine tank every two to three years takes care of it. While the tank is empty, check the brine tank float, the shut-off that sits in a tube inside the tank. Grit around it can make it stick.

Pellets and crystals both make the same strong brine. In a dry room, with the tank kept a quarter to half full, both behave well. Price is a perfectly good reason to choose one.

Rock salt and ice-melt salt: keep them out of the softener

Rock salt is mined and lightly processed, so it still carries the clay and rock it came out of the ground with. Many ice-melt products are rock salt, some blended with other chemicals, and none of that belongs in a brine tank.

On an icy driveway the grit helps your tires. In a softener it settles into a heavy mud on the tank floor. The finest particles get drawn toward the brine line and the injector.

A clogged injector stops the softener from pulling brine, so the salt level stops dropping and the water slowly turns hard. Clearing it is a free job, explained in the injector cleaning guide. Still, whatever rock salt saved at the register, you give back in time and hard water.

Block salt and potassium chloride: two special cases

Block salt is meant only for softeners designed to hold a solid block in the water. In a standard brine tank a block exposes too little surface to make a full batch of brine between cycles. That's why many manuals list it under salts to avoid.

Potassium chloride softens water the same way, trading potassium for the hardness minerals instead of sodium. By the Water Quality Association's ratio, sodium-based softening of 10 gpg water adds about 79 mg/L of sodium, roughly 19 mg in an 8-ounce glass. The sodium in softened water guide covers those numbers. Potassium chloride costs more per bag, and the softener's settings may need adjusting for it, as the potassium chloride guide works through.

Buying, storing and switching salt

Most hardware stores, home centers, farm stores and warehouse clubs carry softener salt, and some dealers deliver it. Prices run roughly $7 to $12 per 40-pound bag, so check current prices locally. Bag sizes vary, so compare the price per pound. The cheapest safe choice is usually solar crystals, and delivery costs more but saves the carrying.

A few habits keep any salt behaving well:

• Check the tank once a month. Keep it a quarter to half full, with salt always sitting above the water line.
• Add one bag at a time instead of filling to the rim. Salt that sits for months in a humid basement is the salt that crusts.
• Store spare bags off the floor in a dry spot, so they don't soak up moisture before they're used.
• Switch types without emptying the tank. Let the old salt drop until you can see the water line, then pour the new bag on top. Don't let it run all the way down, or you'll be reading about a softener that ran out of salt.