Hang-On Filters are a type of aquarium filter designed to be mounted on the outside of a fish tank. They work by drawing water from the tank, filtering it through various media, and then returning the clean water back into the aquarium. This design helps maintain water quality and provides a healthy environment for aquatic life. These filters are popular among aquarium enthusiasts due to their ease of installation and maintenance. They typically include features like adjustable flow rates and multiple filtration stages, which can include mechanical, chemical, and biological filtration to effectively remove impurities from the water.