Deck on north side of house. I have a very small fairly new deck that covers up a cement stoop with about 4 steps. It is made with pressurized lumber, and ONE of the planks right in the center of the deck, from end to end, has a mold or algae problem, green anyway, with moss between cracks. I have scrubbed with household bleach, with H2O2, used a pressure washer and removed surface moss, but there are still streaks of green throughout the plank. I coated the deck annually with a transparent deck finish. Is that hindering the cleaning? Should I sand that one plank? Or try something else?