We inherited a pool when we bought our house and while everything works great, I've always noticed what looked like hard water stains all over the plaster. No matter what brush I used there was nothing that worked to get rid of it or even diminish the definition. I've had to drain the pool and was thinking, GREAT! Now I can sand it out. Nope. Nothing. I don't have the budget to replaster or resurface, but does anyone know what this is, what caused it, and if there's anything (besides resurfacing) I can do? The pool store wasn't sure. (See attached photos)IMG_1784.jpg
The pool was built in 2008 I believe.
Thanks for any advice.