Join Date: Sep 2020
Location: Durham, NC / Clarksville, VA
Brianna, if your pics are of the same stair tread, before and after stripping and sanding (as they seem to be), I think the black in the "after" pic could be the grit from your sandpaper sticking to the gummy wood.
I've used quite a few strippers over the years, and the current version of Citristrip seems to be awfully gooey and difficult to remove completely. If there was any amount of that left in the grooves of the wood where the paint had worn off, your sandpaper may have been fine enough to just clog up the grain. What grit of sandpaper were you using?
I'd let it all dry completely, since you mentioned you'd taken another shot at it with the Citristrip. Then use a heavier grit sandpaper as others have suggested. I'm taking paint and stain off old windows and doors and I'm using 80 or even 60 grit at times to get the last of the stain off. Then work your way back up to a higher grit, appropriate for whatever finish you're going to apply.
Good luck, and happy house restoring!