Penn-Plax presents the Cascade 170 Filter Replacement Bio-Sponges. These Bio-Sponges are specifically designed for the Cascade 170 Fully Submersible Internal Filter (CIF4), and serve as a replacement for when it's time to cycle out filter media. The Bio-Sponges aid with keeping the water inside your tank crystal clean, allowing for a safe and healthy environment. Physical & Biological Filtration: This replacement Bio-Sponges optimize the colonization of anaerobic bacteria, along with providing mechanical filtration that traps large particulate matter. 2-Pack: The package contains two Bio-Sponges. Although they are disposable, they can be reused time and time again. Simply clean the Bio-Sponges in a separate container with some of your aquarium's water. This allows for the colony of anaerobic bacteria to remain intact within the Bio-Sponges. Measurements: 1. 2” (L) x 1. 3” (D) x 1. 6” (H) each. Shop Penn-Plax for All Your Pet's Needs: Penn-Plax is a manufacturer and distributor of top quality pet supplies, who specialize in creating excellent pet products for animals, both great and small.