I've never pre-mixed or diluted the acid simply because I feel like I'd be handling it one extra time and thus one more chance for a spill or splash. I don't know if it's been mentioned yet but I always open the jug outside next to the pool rather than inside the garage where I store it. Again: fumes, spills and splashes inside the garage--that would be bad.

Plus, acid washed jeans aren't cool anymore!