Bubble Bios are the world's first Aquarium Moving Media Filters based on industrial MBBR (Moving Bed Biofilm Reactor) technology, which is the relatively recent technology working at the waste water treatment and RAS (recirculating aquaculture system) system. All Bubble Bios have cleanable air diffusers which can give fine bubbles into the filters powered by aquarium air pumps. These air bubbles can give essential oxygen to the filter media and also make moving filter media always rolling which can make auto cleaning. As a result, Bubble Bios will do excellent biofiltration and give convenience to you. All models have bottom filter sponges, but ZBS-200 and ZBS-150 have fine gravels furthermore in the bottom parts, so these can be sit down naturally and do double physical filtration also.