The internet didn't give up any information at all about it. Not showing on the Home Depot site. So kind of suspect. Some brands include a listing of the actual chemical compositions. If there is a manufacturer listed, you may be able to google their site, and get to the required MSDS info, that should give more details about how pure it really is, what else is in it, etc.
Totally 100% pure is VERY expensive (lab/food quality). Most (even pool stores) are between 84% and 97%. The remainder is mostly sodium chloride and other salts, residue from the refining process. Not to be confused with blends, that have a LOT of stuff we don't want added.
In my case, my community actually softens the water for all residents (!) Being vinyl, I usually don't care. But will be adding CH this year, so that I get the water perfect for the coming new heater warranty...at least initially.