After a long wet winter with lots of rain and snow I have grown quit a crop of moss and other green and black CRAP. I preasure washed the decks and top house with good results but my canvas is a mess. What is the best method of cleaning canvas of the green crud and after it's cleaned off what is the best way to slow down this annual growth. Both on the deck as well as the canvas? By the way I'm talking about over 100 inches of rain here in S.E. Alaska!