BLACK SPOTS ON MAHOGANY PORCH

I have a Mahogany porch that is covered. I get about 3-4 hours of sun a day. I am the second owner of the house. I have been in the house for 5 years and haven't done a thing with the porch. I have no idea when the previous owner did anything to the porch. I have decided to go with the Penofin product. I used the Penofin Stripper, Cleaner and Brightener. I did not like the look of it after due to some left over stain in the wood. So I sand the porch with 80 grit. The porch looked awesome. Penofin recommended that I use the brightener after I sanded. Very bad idea. The wood now has gray and blackish spots on the wood and next to the seams. I have added a few pictures to show what I am talking about. Does anyone know what this is or what is causing this? If so, what will fix this or do I need to sand again? 2 pictures is what it looks like now. The one picture is what it looked like after I sanded it.