I'm going to go out on a limb and just take a crazy wild guess and predict that the top two recommendations you're bound to see will be
1. 100% Poly-fill (what I filled the bottom two trays when I ran a 404)
2. Purigen (personally never used it but have heard rave reviews from members)
Either way, two trays of biomax rings along with the surface area of the foam pads should be more than enough bio filtration.
75g Planted Barbs Denison, BlackRuby, Tiger, Albino Tiger, Green Tiger, Cherry, Gold, Checkered, Odessa.
NonBarbs Cardinal, Neon, RummyNose, Bloodfin Tetras, Z. Danios. 1RTS. Amano, Bamboo, Ghost & RCS. 20g Long Shrimp Tank RCS, Tiger, Amano.