Honestly, some people should just sit on their hands when they don't know what they are talking about.
Any sand that is made up from calcium carbonate mineral (such as aragonite sand) holds a lasting reservoir of calcium carbonate, which is slowly but constantly released, and will buffer and raise the pH of ones tank water on a continuous basis. Using aragonite sand can raise the pH to as high as 8.2. Some of the sand formulas that the OP is using (Geo System) are known to raise the buffering capacity & pH of tap water. As long as there is sand in the tank, it will continue to buffer the water. Ditto to crushed coral, crushed oyster shell, etc. In an area with water values such as Vancouver/Victoria, you simply need to replenish over time as these substances dissolve. This is all common knowledge to anyone that keeps fish & lives in this area.
As far as pH shock, it is indeed a myth, when fish die from osmotic shock it's due to a sudden change in TDS, not pH. This was all explained in great detail in this past discussion. I guess some people still don't get it.
http://www.monsterfishkeepers.com/forums/showthread.php?415333-Reverse-osmosis-for-rays
.... and again here.
http://www.monsterfishkeepers.com/forums/showthread.php?415754-PH-shock-vs-Tds-Shock
Osmoregulation has nothing to do with pH, and everything to do with controlling the balance of water/salt concentrations. pH has nothing to do with regards to if ones water is a hypertonic solution, hypotonic solution, or if it's isotonic. The shock part of the equation comes in when a fish has difficulty reaching equilibrium.
Crazyfish - Say hello to Kevin & Dave for me.
HTH