A single-sponge filter is a type of mechanical aquarium filter used in aquariums and aquaculture systems for water filtration. It consists of a plastic or ceramic container housing a spongy material. Water is drawn up through the sponge, which traps debris and waste. The sponge also provides a large surface area for beneficial bacteria, which help to break down fish waste and other organic matter and keep the aquarium water clean. The filter is designed to be easy to clean and maintain, and is an effective and economical way to keep aquarium water clean and clear.