What Is Solar Salt, and Can It Go in Your Pool?

Solar salt is sodium chloride made by letting the sun and wind evaporate seawater or natural brine in shallow ponds. It is one of the cleaner salts you can buy, and plain solar crystals sold for water softeners are fine for most salt chlorinators. The catch is the word “plain.” Softener bags with rust or iron fighting additives, and rock salt, are the ones to leave on the shelf.

This page is part of our salt water pools hub. Below is what separates solar salt from the other kinds, what the chlorinator manuals actually ask for, and how to read a bag before you pour it in.

What solar salt is

The US Geological Survey sorts salt by how it is made. Its salt yearbook describes solar salt as coming “from solar evaporation of seawater, landlocked bodies of saline water, or primary or byproduct brines.” The same report lists the other main types: rock salt, mined from underground halite deposits, and vacuum pan salt, made by mechanical evaporation of a purified brine.

One major producer’s sell sheet for its solar softener crystals sums up the process as made with “sun, wind and time”. The same sheet lists sodium chloride at 99.6% (dry basis), water insolubles at 100 ppm, and says the product “contains no additives.”

Solar salt vs rock salt vs evaporated salt

A water softener maker’s salt guide says rock salts “contain higher levels of insoluble minerals” and calls solar salt “a very clean salt.” The USGS notes vacuum pan salt is the most expensive “because of its purity and the higher energy costs involved in processing.”

We could not find a published insoluble figure for rock salt from a source we trust, so we are not printing one. The manuals give the reason plainly enough: rock salt carries insoluble impurities, and they end up in your pool.

What the chlorinator manuals require

Every manual we read asks for sodium chloride with nothing added. They do not agree on the details.

Hayward’s manual says to “use only sodium chloride (NaCl) salt that is greater than 99% pure” and names bags labeled “Coarse Solar Salt” and water conditioning pellets as acceptable. It then says: “Do not use rock salt, salt with yellow prussiate of soda, salt with anti-caking additives, or iodized salt.”

One Pentair guide sets a higher bar: “at least 99.8% pure NaCl,” with “evaporated, granulated, food quality, non-iodized salt with no additives” as its preferred choice. It warns that anti-caking agents like yellow prussiate of soda “can cause some discoloration of fittings and surface finishes,” that rock salt’s “insoluble impurities” can shorten the unit’s life, and that softener pellets “could damage pool plaster and other surfaces.”

So one manufacturer lists softener pellets as fine and another warns they could damage plaster. And a solar salt listed at 99.6% clears Hayward’s 99% line but sits below Pentair’s 99.8% on paper. Go by your own unit’s manual. If it asks for 99.8%, buy salt whose bag or spec sheet says so, or use evaporated salt. If it asks for 99%, plain solar crystals meet it.

Here is what the impurity limit means in pounds. Filling a 10,000 gallon pool from 0 to 3,200 ppm takes about 267 lb of salt (run your own numbers here). At 99.6% purity, about 1 lb of that is something other than sodium chloride (267 x 0.004 = 1.07), and at 100 ppm of insolubles, less than half an ounce will not dissolve. Small, but not zero, and it goes in again with every top-up.

Can you use water softener salt in a pool?

Yes, if it is plain sodium chloride. Hayward’s manual names “common food quality or water softener salt” as the kind to use. “Pool salt” is not a separate chemical. What matters is purity and what else is in the bag.

The trap is the softener salt sold for iron problems. One producer’s sell sheet for an iron fighting pellet lists citric acid at 0.35%, “an iron complexing agent,” and says the pellets may contain sodium hexametaphosphate to resist “mushing and bridging” in the brine tank. Those extras are there for the softener, not your pool. None of the chlorinator manuals we read allows additives, and the preferred salt in Pentair’s guide is explicitly “with no additives.” Sodium hexametaphosphate is a phosphate, and Orenda’s technical blog explains that under the right conditions calcium binds to phosphate and forms scale. You do not want to dose your pool with a product built to strip metals out of a different machine.

Potassium chloride softener salt is also out. Pentair’s guide says: “Do not use calcium chloride or potassium chloride as a source of salt.”

Why rock salt and iron cause stains

Rock salt is the one type every manual we read rules out. Iron is part of the reason stains show up. Orenda notes that iron “tends to turn orange/brown/red when oxidized” and that chlorine oxidizes it, so the rust can drop out of the water and settle on surfaces. A salt pool always has chlorine in it, so any iron you add has a good chance of ending up as a mark on the floor. If you already have one, see our guide to brown stains in a salt water pool.

Dissolve it before you trust the panel

The salt reading on your control panel does not come from a salt sensor. The unit measures how easily current crosses the cell and infers a salinity number from that. Salt sitting undissolved on the floor does not conduct anything, so the panel reads low until it is all in solution. Pentair notes that pellets “will take longer to dissolve” than granulated salt.

People see a low number an hour after adding salt, add more, and end up over target. Brush the salt around, run the pump, and wait until the floor is clean before you retest. Then confirm with an independent salt test kit rather than the panel alone. Our guide on how to operate a salt water pool covers the startup order in full.

Check the bag

• Sodium chloride only. Not potassium chloride, not calcium chloride.
• Purity at or above what your manual asks for. Look for a stated percentage, 99% or 99.8% depending on your unit.
• No iron, rust or resin cleaning additives. A softener bag that promises to fight rust or iron has something added.
• No yellow prussiate of soda (also listed as sodium ferrocyanide or YPS), and no other anti-caking agent.
• Not iodized.
• Not rock salt.

Once the pool is at target you will not buy much. Salt only leaves with water, so read up on how much salt a pool uses per month before you stock up. For target levels, see our salt levels guide. And if you are wondering how salty 3,200 ppm really is, our page on saltwater vs freshwater pools puts it next to the ocean and your tap.

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