Costco, at my location, only carries the Clorox with the polymer additive (Chloromax). Walmart has their Pool Essentials brand of liquid chlorine available at a good price during the summer. I use either the Great Value bleach or their Cleaning Bleach when Pool Essentials isn't in store. HD's HDX pool chlorine or Lowes Kemtech are fine too. Google liquid chlorine with your hometown and you may get some pool stores near you that have it.