I am guessing my deck is roughly 15-20yrs old. It has had a semi transparent stain on it for 2/3 of its existance. The finish is weathered and falling off in spots. I don't know if I should sand it first, or use a stripper. It will need some sanding to smooth out a few areas. Suggestions.

Due to how old the deck is it may be made using CCA lumber. I hear it is bad to sand or wash such a deck if that is the case.

I am open to all advice/suggestions on how to revive my deck. I do plan on replacing all the deck railings, the focus on cleanup is on the deck itself. Thank You!!

I would use a deck stain stripper first to remove as much as possible. If needed I would sand off any stain that the stripper does not remove.

Washing CCA wood is not an issue. Sanding can be an issue if you are over exposed to the dust. I would wear a mask to minimize any of the Arsenic getting into your system.