Something white and crusty stuck to AG liner

I have no idea what it is, maybe some type of calcium, all I know is it WILL NOT come off by scrubbing, so im looking for some advice if anyone has any, I found it after taking the winter cover off this week. This is a 30' round if that matter. Im not the kind of person that puts to many chemicals in my pool, this pool is going on 5 yrs old and mostly ive done nothing but put chlorine in it over that time frame, other than the polyquat recommended before closing, but thats about it

Sounds like calcium scaling...can you test for and post results for CH, TA, and pH?

Janet