With a brush (soft or hard) or even a Scotch-Brite pad, get a can of “BarKeepers Friend” (ever used it?) can be had at most grocery stores and virtually all Wal Marts. It is a very strong cleaner designed for stainless steel and boaters have used for years on their deck as it will remove the berry stains from birds, and other stains well into the porous gel coat that things like acetone, Dawn, or common deck cleaners would have little to no effect. It is a gold can with a blue label and white lettering in the blue box. It is a oxalic acid in a white powder form and wear gloves and eye protection, if your hands are in contact with it for more than a few seconds before washing, they will turn red and feel very hot. Protect the other areas as you apply it. Follow instructions on can. The powder will do nothing until wetted. So mix some up with water, and try a little scrubbing with a slurry. If that doesn’t do it, you can leave a slurry or paste on the surface and it will continue to work until it is dry. West Marine sells….”On & Off” which is I believe if you read the contents, also Oxalic acid based. Ospho gel (because it would work for hours and hours or all day without drying, was the best (WM sold as well, but it may not be avail anymore or in certain states). It would take a grey not skid deck that had turned to a salmon or taupe/beige over the course of 20 years and bring it back to the original grey, without multiple apps. (why it may have been banned in some areas, as it worked too well and no doubt would not be friendly if just hosed off into the water)
I only had to use the “BarKeepers Friend” and a moderate amount of elbow grease to banish the stains. See my before and after pics below.
