EHEIM Pro 4+ Canister Filter Pads will ensure that your finned friends always have a crystal clear water column. Designed for both mechanical and biological filtration， both fine and coarse pads are provided. They are suitable for use in either freshwater or saltwater environments and create exceptional conditions for the colonization of bacteria cultures. Constructed using porous materials， water is distributed evenly throughout the pads while dirt particles are trapped and removed. They are reusable and can be cleaned while still maintaining beneficial bacteria.