This is an acrylic box that is designed to sit on top of a sump or refugium to act as a trickle filter for low-flow filtration. You can use a number of different media options like filter pads or filter floss, carbon, chemipure or purigen packs, anything that fits into a tray. Trays are not included but you can use the egg-crate frag rack material to make some cheap shelves. Or cut some holes in a piece of acrylic and have a holder for a bunch of filter socks. WYSIWYG!