Yup, the 4#+ box is the standard size. I'm going to guess your pool is around 24,000 gal, so you might want to start with 2 boxes. Adding thru the skimmer is fine. You can broadcast CaHypo at the same time, but be aware that the CaHypo may make your pool somewhat cloudy. Plain, unscented bleach is the way to go if you want to impact the clarity the least.

Michael