My San Juan builder/dealer told me that calcium was not needed in a fiberglass pool (or a vinyl pool) but told me to keep the calcium levels same as gunite since I have an acrylic spillover spa with a marble spillway and grouted tilework all around the spa that the water cascasdes down when the spillover is operating for the sake of the tilework and spillover. (and I have a heater). My builder specializes in fiberglass but he installs all 3 types of pools. San Juan recommends 200-400 ppm calcium for their pools in their maintenance manual.