Aqueon EcoRenew Replacement Filter Cartridges are dual-sided, featuring fibers made from sustainable materials infused with carbon. This sustainable material allows these cartridges to be Eco-Friendly being both biodegradable and compostable. The EcoRenew cartridges also feature a NoDrip design to help eliminate extra water mess when changing your filter cartridges. Due to the sustainable nature of the EcoRenew cartridge, it is recommended to replace BEFORE is starts to decompose-approximately 4 weeks. Neutralizes the chlorine and chloramines typically found in tap water, making it safe for fish. Helps to reduce the stress on fish as they become familiar with their new environment. Helps restore the natural slime coat to skin and gills, which can be worn away from netting and transporting fish.