Prefilter sock 4″; 200 micron. Absolute filter socks give the best qualities of trapping free floating debris to give your tanks water that crystal clear appearance. In most cases we will always put it in our sumps. Filter Socks are used on overflows to remove small floating particles from aquarium water. This can dramatically improve water quality and reduce maintenance on filters that would otherwise become clogged. Absolute Filter Sock is better at removing particles than mesh but can clog faster. 200 Micron Filter sock.