Bead filters are a type of filtration system that is commonly used in koi ponds. They work by filtering water through a bed of small, plastic beads that have a high surface area. The beads are typically coated with a biological filter media, which helps to remove impurities and promote the growth of beneficial bacteria. Bead filters are highly effective at maintaining water quality in koi ponds, and they are relatively easy to maintain. They can be used in conjunction with other filtration methods, such as mechanical filters and UV sterilizers, to provide a comprehensive filtration system for your koi pond.