Not sure where you saw surface debris but I dont have any or skum. I have plenty of surface agitation and flow. MP10 on about 20% makes everything move well. When I do maintenance I bump it to 40% to really get stuff up and out.I didn't read through all these pages, but from your initial post you have surface debris.
You need more flow and flow that will agitate the surface. That won't fix the slime on the surface, but a good protein skimmer will.
Nitrates, what test are you using? Any filter media like Marine Pure balls or Brightwell media? Too much media will lower nitrates to 0. So if you want them to come up, you'll need to remove about half if the media and see how that works.
No bio media or skimmer, just floss. I tried bio media at one point but realized I didn't need it and removed it.