I have two seachem bags filled with 250ml of purigen per... I would say that tray is only 40-50% full. I'm really looking for a bag that is circular and not square/rectangle like the bags I have now. They are nice bags so don't be me wrong, but would be nice to have a monster circular bag that could hold 1L of purigen (like the shape of a marble bag). I can see my stuff not really getting good flow because the water will be able to channel around the bags in that big of a basket. I was thinking about putting a blank in there of sorts that would restrict the flow a tad and better force it through the purigen bags in a more dispersed manner (something like a little tire/donut made of polystyrene or something to leave only a center ring to stuff the bags into).
Bottom: 2-3x Purigen bags (could add 1x carbon or other as needed)
Middle: Bio balls with a FX Fine Filter Pad on top (Blue)
Top: Fluval Ceramic media with Black Bio Foam filter that comes with FX6 on top
Really the beads should be on top of the filter pad... but that's to much work. I would prob put bio balls on top with the black filter on top of that.
Search amazon for the big off-brand filter packs that have a lot of reviews. Can't go wrong because it costs next to nothing to cycle the fliters out in series so you always leave some media in there to replenish your biofiltering. The filter media on the outside filters is pretty decent in terms of bio... you will see that if you replace all at once with new.