Tidal 55 Matrix 250ml Matrix™ is a high-porosity biomedia that provides efficient biofiltration for nitrogenous waste removal. Each Tidal™ filter comes with a bag of Matrix™ to get you started. Each Matrix ™ 35, 55, 75 and 110 is pre-packaged in Seachem Zip bags, which feature durable seams and a heavy-duty zipper.