I recently ran out of the 5 gallon pail of pool store 12.5% Chlorine so grabbed 2 bottles of Wallyworld brand 6%. Last night I put in what I think was similar amounts of 6% compared to what I normally do with the 12.5%. Interesting thing is, late this morning I checked the Cl level and it was twice as high as I get with the bulk amount. Now I feel the need to do a controlled experiment to see if it was a fluke or if the pool store stuff is not as potent as I thought. Time will tell.