The api nexx extension is an extension for the nexx external filterr the extension includes a connection kit and filter mediar the api rena nexx extension gives not only filtration but also flexibility in your filterr add one extension to increase filter capacity up to a 400 litre aquarium or add two extensions to increase capacity to a 600 litre aquariumr the pump is adjustable and does not need to be updatedr therena nexx extension is a module filter that grows with your interest and all