The Aqua One 4c Carbon Cartridge is a disposable filter cartridge for use in the Aquastyle (AR) 850 aquarium. The 4c Carbon cartridges form the top layer of the trickle filter. A pack of two Aqua One 4c Carbon Cartridges are supplied (for one full filter change) and the cartridges should be removed and discarded when blocked with fish waste and debris. This will usually be every four to six weeks. The Polymer ‘wool’ layer traps debris while the activated carbon removes odours and clarifies the water. An essential part of the Aqua One trickle-filter system.