Lowes in my area carries the Morton pool salt but they are more expensive than 2 grocery chains in my area that also carry it (Publix and Winn Dixie). Any plain water softener salt (pellet or solar) that is at least 99.5% pure and has no additives for removing iron or cleaning your water softener will work just fine. Pellets are slower to dissolve but with a bit of brushing it doesn't take that long.