Can't add more polygons after import

I had some really messed up polygons on a sculpt I was doing in sculptris so I decided to try fixing it in Blender. I ended up have to delete a lot of messed up polygons and manually replace the polygons in blender. When I finally got it to export back into sculptris as a .obj I tried adding more detail with the inverse reduce brush… but it wouldn’t work, I can only reduce polygons now. How do I restore the functionality of adding polygons?

Did the detail slider move all the way to the left when it opened?