An aquarium sump is a separate tank or container 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 can also serve as a refuge for aquatic life, such as macroalgae or small invertebrates, which can help maintain a balanced ecosystem. By using a sump, aquarium owners can keep their main tank cleaner and reduce the frequency of maintenance tasks.