Problem With Fir Floor

[ThisGuy5280]

I started messing around with an area that had some light-colored horizontal spots by using 80 grit sandpaper with a rotary sander attached to a drill to remove the polyurethane. I then applied stain, and oddly, the original problem is gone but I know have a light-colored area in a slightly different section.
Any suggestions? Do I have to take it down to bare wood?
Thanks.

 

[Ernesto]

Looks like edger marks from the previous sanding job. My answer is yes. Nick ?

 

[Nick]

I would use a Drum on it , then a rotary .. using a drill , or belt sander is just going to put edge marks in the floor ..

 

[ThisGuy5280]

Okay, but should I go to bare wood?

 

[Nick]

You will suing the drum .. Let me know if you want the paper sequence ..