The order of media in these trays from bottom to top is
Bottom Tray – 1 Blue course sponge with 1 white filter pad on top of it.
Bottom Middle Tray – Carbon with 1 white fine filter pad on top of it.
Top Middle Tray – Bio media. Ceramic rings and/or Bio Balls.
Top Tray – Bio media. Ceramic rings and/or Bio Balls (optional* white fine filter pad on top of top tray.)