Fluval Betta Diffusion Chamber Pad, 4-Pack. Designed for use with the Fluval Betta Premium Aquarium Kit, the Diffusion Chamber Pad is a 2-in-1 mechanical media that both diffuses and polishes water during the final stage of filtration. Mechanical filter media Specifically designed for the Betta Premium Aquarium Kit 2.6 US Gal / 10 L 2-in-1 water diffuser and polisher Customized to fit seamlessly within Diffusion Chamber (no water bypass) For best results, replace monthly Size: 4-Pack