Dymax Blue Mat Is Made Of Quality Non-Toxic Material For Both Biological And Mechanical Filtration. Enhances Good Water Quality As A Filter Media As A Site For Beneficial Bacteria, And Efficient As A Mechanical Filter Medium (Trapping Loose Particles Of Debris). Suitable For Both Freshwater And Marine Aquarium. Can Be Washed And Re-Used (Rinse In Tank Water - Not Tap Water - To Maintain Its Use As A Biological Filter).