Pool Salt: What to Buy, What to Avoid, and What It Should Cost

Pool salt is sodium chloride. That is the whole product. There is no pool-specific chemistry in the bag, which is why the most useful thing on this page is a list of the things that must not be in it, and a note about what you are paying extra for when the bag says “pool” on the front.

If you already know what to buy and just need a number of bags, go to the pool salt calculator.

What the spec actually is

Every manufacturer asks for the same thing. Hayward’s AquaRite manual states it about as plainly as it can be stated: “It is important to use only sodium chloride (NaCl) salt that is greater than 99% pure.” Royal Swimming Pools gives the same 99% figure. The Trouble Free Pool wiki asks for 99.4% or better.

So the spec is: at least 99% sodium chloride, nothing else in it. Bags sold as pool salt are usually 99.8%, which is comfortably inside the requirement but not a different category of product.

Purity matters for a mundane reason. The missing fraction of a percent is minerals and insoluble grit, and the two that cause trouble are iron and calcium. Iron stains plaster and liners. Calcium adds to hardness you may already be fighting. At 99.8% in a 40 lb bag you are adding about an ounce and a half of everything-that-is-not-salt, which is why the high-purity bags are worth buying but not worth hunting for.

Water softener salt: the answer your pool store will not give you

Hayward’s own manual names it. The acceptable types listed are “common food quality or water softener salt,” and it adds that “it is also acceptable to use water conditioning salt pellets.” The Trouble Free Pool wiki goes further and recommends solar salt sold for water softeners as the default choice, noting that pool store salt generally costs more for the same thing.

Two honest caveats, because this is not a free lunch.

Check the bag, every time. Softener salt is where additives live. Rust-inhibitor and iron-fighting formulations are sold right next to the plain ones, in near-identical bags, and those are the ones to leave on the shelf. If the bag lists anything other than sodium chloride, put it back.

Pellets dissolve slowly. They are compressed for a brine tank, not for broadcasting across a pool floor. They work, and Hayward says so, but expect to brush for longer and wait a day or two before you trust a test. Crystal or granular forms dissolve noticeably faster. If you are topping up a few hundred ppm before a weekend, the faster-dissolving bag is worth the premium.

The four things that must not be in the bag

This is the list from Hayward’s manual, and it is short enough to memorize: “Do not use rock salt, salt with yellow prussiate of soda, salt with anti-caking additives, or iodized salt.”

Rock salt. Mined, unwashed, and the cheapest thing on the pallet in winter. The impurity load is the problem, not the salt. It is full of the insoluble grit and iron that the purity spec exists to keep out, and it leaves a residue on the floor that never goes away.

Yellow prussiate of soda. Sodium ferrocyanide, an anti-caking agent. Royal Swimming Pools puts a number on the tolerance, saying to avoid salt with more than 1% of it. It is an iron-bearing compound going into a pool with an electrified metal cell in the plumbing, which is reason enough to avoid it entirely rather than argue about thresholds.

Anti-caking additives generally. They exist so a bag does not turn into a brick in a damp garage. Nothing in that job description is good for your water.

Iodized salt. Hayward capitalizes this one. Iodide and a chlorine generator produce iodine, and iodine stains. Table salt also carries anti-caking agents, so it fails twice. It is an expensive way to salt a pool regardless.

Ice melt deserves its own line because it is seasonally cheap and sitting right there. Most of it is rock salt, some of it is calcium chloride or magnesium chloride rather than sodium chloride at all, and the blended products carry colorants and anti-caking agents. It fails on every count.

What you should be paying

A 40 lb bag runs roughly $10 to $25 depending on whether the bag says pool on it, what time of year it is, and how far the pallet travelled. Softener salt of the same purity sits at the lower end of that, which is the Trouble Free Pool point about pool store salt costing more.

Worth framing the spend correctly. Salt is the cheapest thing in a salt pool and it is not consumed, so the annual bill is small and lumpy: a large startup dose once, then top-ups for water you lose. Startup figures from River Pools run $72 for a small pool, $180 for a medium one and $270 or more for a large one. Everything expensive about a salt pool is the equipment, which is covered in salt water pools.

Buy on purity and dissolve speed, not on branding, and do not drive across town to save $3 a bag.

How much you need

One 40 lb bag raises 10,000 gallons by about 480 ppm. The target is whatever your manufacturer specifies, which for Hayward is “between 2700-3400 ppm (parts per million) with 3200 ppm being optimal.”

Two rules that prevent most of the bad outcomes. Add half, wait a day, then test, because salt needs time to dissolve and distribute and a reading taken two hours after pouring tells you nothing. And brush it off the floor, because salt dumped in one spot stays in one spot. One owner put twelve 40 lb bags into a pool they believed was 8,403 gallons and still read 500 ppm; the reply from Inyo was to go and recalculate the pool size.

That is the real lesson. Almost every “I added six bags and nothing happened” story is a wrong volume, not a bad bag of salt. Get the gallons right first with the pool volume calculator, then use the salt calculator for the dose.

Before you buy another bag, check whether you need it

This is the part that costs people real money, so it goes on the page about buying salt.

Almost no residential salt chlorine generator has a salt sensor in it. It has a cell with metal plates, and it watches how easily current crosses the water between them, then infers a salinity figure adjusted for temperature. The support knowledge base at Poolside describes most systems as estimating “salt levels using an algorithm” rather than reading salinity directly.

So anything that changes how well your cell conducts changes the number on the display while no salt moves anywhere: scale on the plates, worn plates at the end of their life, cold water in spring, low flow or air in the line, or the wrong cell model selected in the control menu. That last one rescales the entire reading and is a thirty second fix that people chase for weeks.

The failure pattern is predictable. A cell nearing the end of its life under-reports. The owner trusts the display and adds salt. The reading barely moves, because salt was never the problem, so they add more. Now the water is at 5,000 ppm, the cell still says LOW, and they need a partial drain and a new cell. One owner on Inyo’s guide to reducing salt said it directly: “I added to much salt to my 15000 gallon pool because I did not realize my T-cell was going bad.” Another on the same page gave the cleanest evidence of instrument drift you could ask for: “Turned on old cell for one last reading. It was 2500. Put in new cell and it said 3600.”

Replacement cells are not a rounding error. Leslie’s pricing has a Hayward T-CELL-9 at $899, a T-CELL-15 at $1,099, a Pentair IntelliChlor Plus40 at $1,819 and a Jandy AquaPure 1400 at $1,949, and River Pools puts a typical well-maintained cell at three to seven years and $700 to $1,100 to replace.

So before the third bag goes in to satisfy a display, confirm the display is telling the truth. The procedure for that is in salt levels and testing, and the cell side of it is in salt cells and water care.

Where salt goes, and where it does not

Your cell does not consume salt. Salt becomes chlorine, chlorine sanitizes and reverts to chloride, the cell converts it again. Salt leaves only with water: splash-out, backwash, filter cleaning, leaks and draining. Rain and top-ups dilute it.

Which means a pool that needs a bag every two weeks does not have a chemistry problem, it has a leak. And in the other direction, if your fill water is salty or very hard, every top-up adds a little and the level can drift upward over years with nothing ever added deliberately. Test your fill water once. It takes ten minutes and explains a lot of confusing histories.

If you have overshot, dilution is the only lever, and the drain-down planner works out how much water to replace and where the rest of your chemistry lands afterward.

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