I have just finished tiling my concrete swimming pool (it used to be plaster). So now I have beautiful mosaic glass tiles and epoxy grout. I just filled it with water a couple of days ago and now ready to do the proper balancing. I will definitely go to the local pool store for testing the water and purchasing the necessary chemicals but based on their feedback I am not sure why would I still need to add calcium to the pool water.. As I said the pool is a concrete pool, waterproofing was done using Mapelastic 315, then glass tiles, then epoxy grout.. Maybe a little bit of calcium not as much as for the plaster pool? the size of the pool is about 20000 gal.. thanks!