You are making it harder to understand that it is!

It's all the same stuff, just different "proof" as it were.

6% ultra bleach will add half as much chlorine, gallon for gallon as 12% chlorine.

My rule of thumb is if the gallon of12.5% costs MORE than 2 gallons of 6% it's not a good price. If it's less then it's cheaper.

Where you get the carboys mattters. I go to one store that turns it over rapidly--today they had 13 palattes. Whenever I test it, it's usually 14%--stronger than it's sold as.

You'll want to invest in a spigot for the carboys--$4 or $5 but it makes life easy and SAFE! I fill up a gallon jug halfway to add chlorine--to my 20K pool it adds just over 3ppm. If I need to shock, I fill the gallon jug at least twice which adds (drum roll) 12.5 ppm! (unless it's testing a t 14% then it adds 14ppm),

The carboys may be blue but they are "greener" You pay a deposit once and then exchange them. The deposit was like $6 but I just exchange them when I buy new ones and have had 3 for years. They get reused. Plus there's less trash. I have 3 carboys--that like have 30 gallon jugs of 6% bleach!