This BioChem Zorb cartridge is included with all Rena Nexx and SmartFilter aquarium filters. The four-sided cartridge has two layers of mechanical filtration and an inner layer of BioChem Zorb which is a mixture of activated carbon, ammonia removers and scavenger resins. This is the best combination of chemical and mechanical filtration for most aquariums. Also available for the Nexx and SmartFilter; NitraZorb cartridges and PhosZorb cartridges for those wanting to customize the Nexx and SmartFilter cartridge system to suit an aquarium's particular water quality needs.