Along the same lines as a previous post. We also cleaned, brightened and sanded deck, then several weeks of rain so didn't get a chance to stain. We now have black speckles covering many boards of wood. In my past experience I was told that was mold/mildew on the top of the wood. Should we clean and brighten again? How do we get rid of the black speckles? We want to make sure we remove any mold/mildew before putting stain on it.
That might be rust. Try a wood brightener to see if that removes it.