The Atlantic BG2234 is a mesh bag designed for holding together loose biological media. Ideal for use in waterfall filters commonly found in koi ponds. The BG2234 is perfect for use with bioballs, lava rocks, and any other loose filtration media. This media bag measures 18" x 22" and features a drawstring to allow the media inside to be secured. The BG2234 is a genuine replacement bag that is included as an accessory within the Atlantic Filterfalls line of products. However this media bag is universal and can be used in a variety of applications.