If by "mag" you mean magnesium (I'm assuming it's not a brand name), any epsom salt brand should do. The Publix brand looked ok to me from the chemical analysis.
Epson salts is magnesium sulfate heptahydrate. MAG flake is a brand of magnesium chloride hexahydrate sold as a deicer (like Dowflake is). Its easy to find where it snows a lot; I am trying to locate it down here where its not quite so cold. The Home Depot near me doesn't sell it. I am trying to find somewhere down here that does. Using Mag flake prevents the build up over time of sulfate.
