Looking for tips here. I have one that had years of algae and tar buildup. Most of that came off, but is very discolored. Anything out there that will actually make it white again? I tried Greased Lightning, Simple Green, Westley's Bleeche White ( as in whitewalls for your car), and Tarminator. The Tarminator got the creosote off, and the Westleys got off some of the surface dirt. But there are deeply embedded stains.