Black spots all over boat in marina; do I have any recourse? How to clean?

[Hunky Dory]

I have had this problem for years.I have tried soap and water with a stiff brush, to no avail. By accident I found Super Clean which has been around for years. I use the supplied spray bottle and spray the surface, wait a couple of minutes not letting the area dry. Then use a deck brush and water to take the spots off , unbelievable. I need to buy shares in the company as I use gallons of this stuff for everything from cleaning car engines, garage floors, tires, bugs from the front of my car, bilge cleaning and on and on. The cleaner is bio degradable, and it also comes in bulk up to barrel size. You can find the product at Walmart in the auto section. Give it a try!