I have a pool going on 20 years now and I don't know if it is the soil or just age but the white steps and accessories on the pool get a dark dirt coating that just won't come off. I found one cleaner that works but only above the water line. Had an Idea to try MR CLEAN MAGIC ERASERS . They worked great . All my steps and trim are bright white and I know next year it will be an easy job but it took off all dirt stain from years of build up. I used the ones that are white with a blue center they say kitchen scrubbers. They don't last long but in 20 years of trying everything they are the first thing that worked. J.Michael