Actually most salt refined into pure NaCl for table salt is mined. Instant gratification.John, I think most salt is collected from evaporated seawater. With that said, It's a completely unnecessary prophylactic additive. As pointed out, it has its uses as an ich treatment and short term dip. Since there is nothing particularly esoteric inside that API box, I maintain the belief that it resides on the lfs shelves for the primary purpose of separating hobbyists from their cash.
Mark