Under Trees

Hi... I am looking for the best stain/sealer for these conditions. I have 1200 square feet of pressure treated decks, benches and landscape ties. Everything is about 10 years old and still in pretty good condition. I have treated it every few years... I think the last time was about 2 years ago... and some of it 3 years ago. I have pressure washed it with bleach and lomax. It is pretty good at this point but I was going to go over it again with??? What do you recommend? There is the slightest bit of old finish in a few spot and a few spots that appear to be too black. I am in Pa and this deck is under 2 large maple trees and wet leaves often sit on it too long over the winter. I want something that never has to be stripped... I just want to clean it and reapply. Should I use 1 or 2 coats and how much product should I buy? Thanks for your time!