Evolution Aqua K1 filter media is a high performance filter media that provides a large protected surface area. K1 Media provides protected surface area to boost beneficial bacteria colonization for biological filtration. As the K1 Media moves within the filter, it causes old bacteria on the outside to be displaced. This makes space for new, younger, heavier-feeding bacteria to rapidly colonize. Within the wheel is a protected surface which enables colonies of bacteria to naturally follow their lifecycle and then fuel the latter stages of the nitrification cycle. Designed to be self-cleaning.