Run Carbon GFO or any other media in the Red Sea Filter Media Cup. Pack the Red Sea Filter Media Cup with filter floss, ceramic media, carbon, gfo, or any other media you want. The slots at the bottom half of the cup force water to flow down through your media before it can freely exit. With the included media bag, you can manipulate your aquarium\’s water to go through a wide variety of media, carbon to help remove any toxins or yellowing pigments in the water, GFO to help remove phosphates or a biological substrate like MarinePure for the added surface area. The Filter Media Cup is an ideal and cost-effective replacement to filter socks as well. If all you want is to polish the water of free-floating particles, then placing a few handfuls of a filter pad in the cup is all you need to do, merely replace the dirty pads every few days. Replaces filter socks Create your own custom filter tower Works with all Red Sea Reefer & most MAX systems (excluding MAX Nano) Compatible with most pre-made sumps Includes media bag Specifications: Dimensions: 4\” x 8\” Min Sock Opening: 3.5\” Capacity: 1L Media Bag Size: 5\” x 10\” What\’s Included? 1x Filter Media Cup 1x REEF SPEC Media Bag