I was in a local Wal Mart a few days ago and they had a stack of pool chlorine jugs with 11.5% concentration. I think the trade mark was Clorox but I was on another mission and easily distracted.

I got fed up with the lugging ( my wife did too ) and we went to a salt system last year. This is neat. Just lug the salt in once and maybe add a bit once a year as the water goes down on backwashes.

Good luck.