Red Sea's Filter Media Cups are a simpler alternative to standard messy filter socks. This cup easily fits into the sock holder and can be stocked with a wide variety of media, including filter pads, filter floss, biological media, GFO, carbon, and more. For cleaning and maintenance, this cup can be rinsed or washed out in no time at all. Features one liter of volume for storage, with a 4" dia rim and 8" depth. As a bonus, a FREE media bag is included with the cup!