Eheim Carbon Filter Pad for Classic External Filter 2211 (3 Pieces Per Pack) Eheim Carbon Filter Pads are a great way to polish your aquarium water of debris, odors and discoloration They should be replaced every 3-4 weeks for optimum results This sponge material should be positioned as the last stage of filtering Use it immediately after you are finished treating with medications to help restabilize your ecosystem Contains 3 Pieces per pack