The Aqua One 3c Carbon Cartridge is a disposable filter cartridge for use in the AquaStyle (AR) 620, AquaStyle (AR) 620T and AquaMode 900 aquariums. The 3c cartridges form the top layer of the trickle filter. A pack of two 3c cartridges is supplied (one large and one small for one full filter change) and the carbon 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.