I am estimating your pool volume at just over 17K gallons. A 15 ppm shock level should be sufficient (I think the other shock column is for mustard algae victims) and it looks like 4 1/2 gallons should get you just over that, if you're starting from zero. I would maintain that 15 ppm as consistently as you can, brushing daily, watching pressure on filter and cleaning as it indicates.

By the way, have you had the well water tested for metals? Iron is common in well water, and will change the course of this advice, if present....\

Janet