Liner has a very hard film on it. How can I remove?

[Dean]

I had a problem with algae last year. It was "caked" on the bottom of the pool liner. Seems as if the green color is gone, however, there is a very hard film on top of the liner that only seems to come off when scraping with my finger nail. I cannot figure out what this is or why? Is it still algae? Is there chemical that will remove this? It is like a glassy haze all over the bottom of the pool and is driving me crazy.

Tks for any help

Dean