4-Color Pack Matala Pond & Koi Filter Media- 12"x12" The open, highly aerobic tri-dimensional structure of Matala Filter Media promotes healthy water conditions Ease of cleaning in in a wide variety of filter designs. You'll see it featured in every major Pond, Koi & Fish Care Magazine. Mats are self-supporting, form-stable, rigid and non-brittle This is simply the most effective, longest lasting, crush resistant filter material available today!