A powerful combination of Activated Carbon and Ammonia Remover, the AquaClear Zeo-Carb Filter Insert effectively eliminates odors, discoloration and impurities in freshwater aquariums. This potent chemical duo prevents the buildup of toxic ammonia and nitrite, producing clean and healthy aquarium water. Exclusively designed for the AquaClear Power Filter. Available in the following sizes: Filter Insert for AquaClear 20 single or 3 pack Filter Insert for AquaClear 30 3 pack Filter Insert for AquaClear 50 single or 3 pack Filter Insert for AquaClear 70 single or 3 pack Filter Insert for AquaClear 110 single