Buffer will raise pH, as the previous poster stated. However, the best way to raise pH is to aerate the water through circulation for 24 hours or more before doing the water change. If you add to much buffer in an attempt to raise pH, you could end up with an ionic imbalance.
The best protocol would be to mix up your salt water for the water change, then let it sit with a powerhead for at least 24 hours before doing the water change. Then test the alk and pH of the change water. The pH should be somewhat higher that it was right after mixing the salt mix into the water. If the alk is low when you test it, then use the buffer. If the alk is OK, however, then I woudln't recommend using buffer to elevate pH, because you'll be creating an imbalance that over time can cause your Ca level to plummet.
Most quality salt mixes will mix up with the proper levels of Ca and alk, and adding additional buffer for pH support will possibly get your biomineral balance out of kilter. The best way to adjust pH for change water is rigorous agitation with a powerhead (making sure that the surface tension is disrupted by the flow) to aerate the water, which should get your pH up to acceptable levels for the water change.
