For several years I have used Tesco's thin bleach as a chlorine source: with a content of 1.5% sodium hypochlorite it is easy and very safe to handle, and cheap too. However it isn't so good when I need to shock, as I do now: I would need a trailer-full of bottles. So I have bought some 14-15% s/h in five litre containers (about 1.3 US gallons). For shocking I need to use a 5 litre dose.
I am rather wary about how I should handle this. With care, yes. Should I decant and dilute first? Pour directly into the pool? I don't really know how potent this stuff is - yet. Any advice appreciated.