If one is going to shock at high levels using a hypochlorite source of chlorine (bleach, chlorinating liquid, Cal-Hypo, lithium hypochlorite), then one should lower the pH first before doing so. Adding chlorine raises the pH. Though it will come back down when the FC level drops, you don't want the pH to get too high because it can precipitate metals that can cause staining, can cause cloudiness from over-saturation of calcium carbonate, and at much higher pH the active chlorine level goes down significantly.