I'll let those who close their pools advise you on that one, but personally I think that if there were any damage that would be done to your liner, it has already been done. And the higher FC level you close with, the longer it will be before the Cl gets down low enough to let algae grow. I think you would be fine to leave it where it is, but again, I don't close my pool or use a cover--so hopefully one of those who does close pools give you a more informed answer.

Janet