These re-fillable 20″ x 4.5″ 20 micron carbon cartridges are far cheaper to operate than the normal pre-made carbon cartridges.
The cartridge contains almost 2 kilograms of granular carbon, the carbon is available Coal based, Coconut, Silver Nitrate Impregnated and Chloramine Carbon (the Chloramine and Silver carbons cost a bit more).
Carbon types that can be ordered with the Re-fillable cartridge.