The AquaClear AC20/30 BioMax Insert nodes feature a complex pore system where beneficial bacteria can easily establish and flourish. The media shape is specifically designed to permit even water distribution, which prolongs contact time over a wider area for effective biological filtration. For the AquaClear AC20 Power Filter and AquaClear AC30 Power Filter. The Product Manual recommends you replace the the BioMax Insert every 3 months. 1-pack.