Pool manuals (Intex, as you point out) list standard water chemistry parameters without regard to the material of the pool surface. That is wrong, but if you decide to follow manufacturer's recommendations you'll just spend more money, but not do any harm. The saturation of pool water with calcium carbonate is to protect plaster surfaces (and grout in tile), but is not needed for vinyl nor fiberglass though having some calcium hardness for fiberglass can help to prevent cobalt staining.