As long as you're not having some kind of strange water clarity issue or foaming of some kind, low CH in a vinyl pool is generally not a problem per se. If you get a lot of rain water spillover in your area or your fill water is very soft, then it's often a good idea to have some calcium chloride on hand to bump it up if it goes below 50ppm or so. Other than that, there's really no reason to add CH as long as you keep you pH and TA at recommended levels.
Are you testing your own water regularly?