Aqua-Crylic 4" Corner Sock Filter Lids (Add-a-Sock)This hobby is full of people who love to build their own sumps and make their own equipment. That's just the fun part of this hobby. Help them out by offering one of our Add a Sock kits! These kits are made from durable ABS plastic and cell cast acrylic and come in a variety of sizes and inlet sock options. These are cut to size and easy to install into almost any aquarium or box that holds water. Such an easy way to add particulate filtration to any