If you don't have the time to do it yourself, you can hire a deck-maintenance contractor. But the relative newness of this specialty means most of the pros don't have much experience. That makes checking references and visiting past jobs especially crucial. And because most pros have their favorite products, you'll probably have little say about the ones used on your deck. Use finishes designed for decks products meant for siding won't stand up to foot traffic.
Cleaners contain detergent and bleach, and work best on dirt and mildew.
Restorers contain oxalic acid and are ideal for removing tannin streaks and stains around nail- and screwheads in cedar and redwood decks. Whether you use a stripper or cleaner, or both, apply it with a roller or stiff-bristle push broom. Wait a few minutes for the product to soak in. Then rinse with a hose or power washer. Remember to clean the exposed ends of cut deck boards.