Same chemical, just different concentrations. The only 2 things that matter are 1) dosing appropriately based on the % and your size pool, and 2) price. To easily compare prices, $/oz./%. So if wm bleach is $3.25 and pool store is $5.00 and both are 1 gallon, 3.25/128/0.0825 = 30.78 cents per ounce of sodium hypochlorite and 5.00/128/0.12 = 32.55 cents per ounce of sodium hypochlorite. Walmart wins.