TetraFauna ReptoFilter Filter Cartridge refills work effectively to keep water crystal clear and remove odors from terrarium water. These disposable filter cartridges are tough on debris - Ultra-Activate carbon absorbs odors and discoloration, and dense, dual-sided mesh catches debris and waste. They're convenient, fully assembled and ready to use. Use these medium-sized filters with TetraFauna ReptoFilter 20 gallon, Viquarium and Decorative ReptoFilter.