I have a large pressure treated deck that had been built prior to the purchase of my house. The prior owner applied some sort of a stain to the deck immediately prior to me taking ownership, which is about two years at this point.

I would like to refinish the deck, but I am not sure that I will be getting that done this summer, due to time and budget constraints. However, will it harm the deck if I apply another coating of stain to try and keep the deck in good condition?

Also, when I finally decide to refinish the deck do I need to sand it entirely? If I do have to sand it can I use a floor sander? I have read about using a pressure washer on decks, but I am leery of doing any permanent damage. Any help would be much appreciate, since I want to make this deck last as long as possible.