DECK WASHING FOR DUMMIES

See photographs two and 3. I am now planning to refinish the deck once again this summer. See Picture 4 of latest affliction. The blotchy look has fairly dissipated due to weathering from snow/rain (I reside in northern Illinois). What did I do Mistaken previous yr? What do you suggest I make this happen 12 months? Do I utilize the RAD stripper, cl