Filter Media Biological: We offer some of the best biological filter media on the market today. Our open stroma is all natural and coated for longer life. The open stroma disperses water and reduces channeling. It maintains its effectiveness for a much longer time than conventional aggregate media, frees you up and allows you more time to enjoy your fish and pond. Availble in 2'X25'X1.5" thick and 3X'25'X1.5" roll sizes. Also comes in cuts 2'X5' and 3'X5'.