The hard part of tackling this project was timing it with the weather. Once you clean it, you have to wait 2 rain-free days for it to dry out and before you can stain it. We used this deck cleaner and scrubbed and power-washed away. It took most of the day to clean the deck. We could not believe the difference it made.
On the left, you can see the clean wood compared to the pre-cleaned wood on the right: