I am having my oak floors sanded and refinished, as well as the stairway The treads are maple, and even after heavy sanding, there are areas that still seem to have a blackish-haze, particularly towards the back of the tread, where it meets the riser – almost as if the old stain absorbed much deeper in those areas.

Any suggestions?  Should I try some wood bleach to lighten those areas? My stain colour will be a dark brown, so maybe it doesn’t matter if some areas are slightly darker?