Bio-balls are small, spherical plastic structures used in aquarium and pond filtration systems. They provide a large surface area for beneficial bacteria to colonize, which helps break down harmful ammonia and nitrites in the water. This biological filtration process is essential for maintaining a healthy aquatic environment. Typically made from durable, lightweight materials, bio-balls are often placed in the filter compartment of a fish tank or pond filter. They are easy to clean and can be reused, making them a popular choice among aquarists and pond owners for effective water quality management.