I don't agree with pH shock.
I think its more temperature related or disease related.
I also don't think you should tinker with your pH. Said that in the L135 thread, still feel that way. Do think though that you need to figure out why your pH is chaning so much. Its natural for pH to lower a bit over time if water changes are not accomplished frequently enough, this is due to the fish waste products acidifying the water. However, a tank whos pH rises over time has something affecting it and some investigating is required.