Really, there is insufficient evidence to support the use of slightly depressed salinity for extended periods. Salinities in the range you mentioned will not affect parasites (not only are they resistant, but there are strains of both parasites and bacteria, like Vibrio spp, that prefer brackish salinities--i.e. anything below 1.0264). Most stores keep low salinity to save money, not necessarily cut back on parasites. As a result, there is also less of a buffering content overall compared to full strength seawater. Occasional boosts in carbonates/bicarbonates will work, but it will still fall faster due to the lack of other salts. When it comes to shipping, yes, a lower pH is better. It causes the ammonia/ammonium equilibrium to shift toward ammonium, which is far less toxic. The store may purposely lower their pH in some cases for new arrivals, but they shouldn't maintain them like that.
Just as an FYI, raising the pH can be done using things like baking soda (initial pH drop, then moderate rise), aeration, or washing soda (significant rise). Lowering can be done by vinegar, water changes, aeration, carbon dioxide addition (calcium reactor), sodium bisulfite, or hydrochloric acid (out of these, unless you have experience with them, I suggest you only use water changes or strong aeration to lower your pH, otherwise you may make a mistake). Things like oystershell and crushed coral will not really raise the pH because of how insoluble they are in seawater. They work well for that purpose in freshwater, though.
