I have two Fluval 406's hooked up to my aquarium, first one I have:
Top Tray - Floss, Carbon, Clearmax
2nd Tray - Substrat pro
3rd Tray - Substrat Pro
4th Tray - BIOMAX Foam with filter floss on top
Second one:
Top Tray - Floss, Carbon, Purigen, Rowaphos, Clearmax (Won't be using it anymore...