An aquarium sump is a separate tank or container that is used in conjunction with a main aquarium to improve water quality and filtration. It typically sits below the main tank and houses equipment like filters, heaters, and protein skimmers. This setup allows for better water circulation and provides additional space for beneficial bacteria to thrive, which helps break down waste. Sumps also help to maintain stable water levels and can serve as a refuge for aquatic life, such as macroalgae or small invertebrates. By using a sump, aquarium owners can keep their main display tank cleaner and more visually appealing, as the equipment is hidden away.