It really needs to be eyeballed as it varies with how much the Ph is off, how much soil there is and how much surface area is on the top of the soil. From the sound of "just a touch acidic," I'd suggest just a light sprinkling over the surface to start. You can adjust liquids as well so that when they mix with the acidic soil, the Ph averages at the correct level while the soil is wet. Over time, small adjustments in the liquids will eventually affect the soil's Ph.