6yr Never Stained Deck

We live in central Illinois near Champaign. We bought a house with a 6yr pressure treated lumber deck that has never been stained or sealed. It's on the north side of the house and has very little afternoon sun. Lots of algae growth. It's 450 sqft plus the fascia. We have powerwashed but there is still green in the boards. Considering going the Trex route but wanted your opinion if there is any stain that will hold up to yearly powerwashing because of the algae? If so, what is the next step prior to applying the recommende stain? Thanks in advance for your help!