Sandy,

with a gunite pool, you don't have to be too stingy with the bleach. Might fade a swimsuit if you go in when it's 10+ or so but, other than that, it will ensure you actually reach breakpoint.

4.5 gallons should take your pool to around 16ppm. I would consider that minimum to ensure breakpoint (shock).

Again, it'll disappear almost overnite if you have a lot of organics in there.