Yes, I would suggest a media bag for the bio media as it makes it easier to clean. But, you could always stack the media as follows - bottom lattice screen, Ehfi Mech, blue pad or two, Ehfi Substrat Pro (cocoa puff balls), white pad, top lattice screen. Of course, this is assuming you are using the Eheim media. Did your filter come pre-filled with media when you bought it?