I have an older fiberglass pool that was refinished 2 years ago. The sides of the pool are chalking. You rub your hand on the surface and a creamy white chalky material comes off on your hand. I have been told that it is do to low calcium and I’ve also been told you need to use a sequestering agent. Nothing seems to make a different. Something is deteriorating the gelcoat. No one seems to really know how to maintain a fiberglass pool. Does anyone have a similar problem or know what is lacking in the water chemistry?