Aqua One ChemiCarb is activated carbon which is a key chemical component to your filtration system. ChemiCarb acts to remove organic waste from you aquarium without adding phosphates to your water. As it comes in pellet form, it has an increased surface area to maximise absorbtion of minute particles which are held in suspension in your tank water. As your aquarium water passes through the carbon within your filter it traps these small particles in its pores. Activated carbon does have a threshold as to how much organic waste it can absorb, so should be changed every month. ChemiCarb comes with a small draw string bag to keep the carbon pellets contained when added to your filtration system.