Just like the title says. My local water softener company has Duracube and its 99.4% pure or better with no additive or rust inhibitor. It costs $8.90 for a 50lb bag.
I talked to the guy on the phone he said they don't sell pool salt, but its 99.8% pure with no additives. I think it comes in larger flakes or something as opposed to a fine grain that would dissolve quickly. What do you think?