Newb help! What media to use in back of AIO tank?

[miltonkl]

I just got my first tank, a 40 gallon Aquatop Reclife ECO AIO. It comes with 4 little boxes (https://www.aquatop.com/collections...co-40g-tank-stand-combo?variant=8723321520227) where I can put some media. What should I plan to put in there right out of the gate? Should I leave one or two empty in case I need something specific once I'm up and running?

I bought this tank used so it didn't come with anything in them already. Also, the included protein skimmer seems to be missing a part, not sure how vital it is. I have email in to the company to see if they have parts available. I'm still trying to figure out where to put this beast in my house so I haven't filled it up and tested anything yet, just trying to figure out what all I'll need to get started.

 

[blaxsun]

Filter floss in the top (1-2 layers), Chemi-Pure Blue in the middle and some small MarinePure hex spheres in the bottom (if room permits).