I can't tell you how much a bag of "shock" will raise the pH in your pool--a lot depends on your TA level, and whether the "shock" is dichlor or cal-hypo. I can tell you that a 1 gallon jug of 6% bleach in 18K gallons of water will raise your FC by 3.3 ppm, and will have negligible effect on your pH. You might notice an immediate, slight increase, but as the chlorine is used up, the byproducts will negate the increase from the bleach, so the net effect on pH will be zero.