I went to Walmart to stock up on bleach for the summer, but found the bottles are not a gallon and they are 8% which is ok. But since wm are 3.00 for 121 oz and my pool supply store is 3.60 for a gallon of 12.5% I am wondering if I should stay with the pool store or does 4.5% would make a diference? Any take on that? Thanks Dave