I'm new to pool ownership. I have a 16X32 vinyl liner pool. I have some stains and wanted to remove them, when I took my sample to pool store they said my calcium was to low 50 ppm and I needed to add some "calcium hardness increaser". They want me to add 25#'s of this not all at once but over a few hours. I started reading about this process and some people said never add calcium to a vinyl liner, I also spoke to a friend who has had a vinyl liner pool for 10 years and she said she never add calcium. Please help, thanks in advance Sue