[BoomerD]

Most of us agree that Petco sux, but from reading a bit via Google, it appears that it's 100% calcium carbonate...so it's probably aragonite based sand and should be fine for your tank.
DO NOT worry about the buffering effects of the sand. For the sand to start to dissolve enough to buffer, IIRC, the pH of the tank would have to drop far enough that you'd have more problems than anything that the buffering effects of the sand would fix...
I prefer NOT to use silica sand because of the potential of free silica to fuel diatoms, otherwise, the IDEAL sand is sugar-fine "oolitic" sand. Actual chemical composition isn't nearly as important as grain size and shape.
BUT, I'd STILL prefer aragonite sand to silica sand.