What do you mean 'media filter'? They are a filter, they use media.
Flow should always go from course mechanical (foam blocks in the outer ring of the FX5), then fine mechanical (pads or filter floss in the middle of the top tray), then chemical if you use it (middle of the middle tray), and then biological (middle of the bottom tray). If you don't use any chemical you can double up on the biological. I recommend Seachem Matrix biomedia. It is very porous, has more bioavailable surface than stuff like Fluval or Eheim's biomedias, and is reasonably priced (especially since you only have to buy it once).