To figure out ppm per gallon of bleach or LC, you need 3 factors:

1. The PF (pool factor) -- yours is 5.5
2. The % of chlorine in the bleach you have (2, 2.75, 3, 6, 10, 12.5)
3. The approximate weight per gallon -- use 8.5 lbs per gallon for bleach

So, for 6% household bleach, your calculation would be 5.5 x 0.06 x 8.5 = 2.8 ppm / gallon. Usually, I just remember that it's 0.5 lbs Cl2 equivalent per gallon of bleach (0.06 x 8.5), rather than calculating it. So, for 10% bleach, it would be 5.5 x 0.10 x 8.5 = 4.7 ppm, and for 12.5% it would be 5.8 ppm per gallon.

In actual fact, pool store chlorine, except in locations where they have their own bleach tank and get daily deliveries, will only rarely be up to the rated percent. Here's why:



What you are seeing is a pallet of 'liquid chlorine' stored at the doorway of an SCP warehouse at over 90 degrees F. Those pallets come in early May and are stored at warehouse temps for a month or more . . . BEFORE they arrive at the pool store. This picture was taken in May 2011, but there was a pallet sitting in the exact same spot this July, on the day it hit 107! *THAT* bleach probably was less than 4% strength by the time some poor sucker bought it.

It's not deliberate -- I've never talked to anyone at SCP or locally that understood how rapidly bleach breaks down at high temps. But, whether they understand or not, hot bleach still breaks down. By contrast big-box store bleach (a) has to more pure, to avoid laundry problems, so it breaks down more slowly at ANY temp, (b) rapidly transits the supply system, especially at Walmart, and (c) often stored in cooler or even air conditioned areas. So, it's MUCH more likely that 6% Walmart bleach is 6+% than it is that 10% pool store LC is going to be near 10%.