Filter Socks are an essential part of aquarium filtration. They remove excess food, detritus, organic wastes, and other particulates to give you crystal clear water. Specs: 200 Micron Filtration - filters well while also being able to go longer between changes. Standard 4 inch ring - made of high quality thick plastic unlike other socks that use inferior plastics. Fits all 4" filter sock holders. Polyester Felt material - using felt as a filter sock material has it's advantages such as removing micro bubbles from your overflow. Micro bubbles won't pass through the felt material as they would a mesh material. Reusable - When your filter sock needs to be cleaned we include washing instructions in every order to get the most uses out of your socks. *These socks do not fit IceCap sumps
