The green on your deck is caused by persistent moisture, so we can guess your deck is located in the shade. It is probably not mold, but algae. This year in addition to pressure washing which provides moisture the algae thrives on, also brush on a weak solution of bleach to clean the deck. That will kill the algae. After the deck is dried, apply a sealer / stain formulated from linseed or tung oil. That should prevent any regrowth of the algae. If using a water based sealer, be sure to look for biocide or algicide. If not present, find a different product.