Remove these marks from my Redwood Decking.
I bought Redwood boards from the lumber store and they have these black marks all over them. It seems all the boards have these marks to some degree or another, I picked the best ones. I have tried the suggestions that I have found in other posts, but the marks are still there.
I want to stain the deck with Penefin, which I tested a piece and the ink or mildew still shows thru. I have sanded with 60 grit, then 150 grit, and finally 220 grit paper. It feels good and looks good too, but the marks still peek thru, errr!

Any ideas that haven't been posted in other posts?