If there's no fading of your liner, and no strange "feel" to it, then liner degrading isn't the problem. At the time I wrote the post for some reason I was thinking you had a gunite pool....just kind of "thinking out loud".
With a CYA of 50, I'd hold off on shocking to 30--try going to 20 instead. There was one time in the past that I actually shocked mine to almost 40 and held it there for about 3 weeks with no apparent liner damage, but that was a very extreme case and I wouldn't recommend it, just to be on the safe side.
Janet
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