I have white staining on the walls of my two and a half yo BRP, not sure about the rest of the pool as it's only noticeable when the water level drops. Reported to BRP who wanted all the monthly test reports as stated in the warranty otherwise it will be voided, which is BS according to my local pool shop who had a client win a claim for white staining with them, although they are appealing apparently. My last contact with BRP said they'd sent my reports to the gelcoat specialist. As I don't have my pool tested every month I'm sure they will be blaming me. I advised them I don't test during winter as I winterise my pool with a floater and turn off my chlorinator, also during heavy rain which we get plenty of, I won't test till its over as you're just washing the chemicals down the drain, this didn't seem to make any dfference to them.
I'll have to wait for them to get back to me before I take it further