Tetra's TetraTec PRO-II Power Filter Cartridges clean the water three ways; there is a coarse mesh panel to remove medium to large particles, a fine mesh panel to remove fine particles and more Ultra-activated carbon to remove harmful chlorine and chemicals which can cause odors and discoloration. The patented cartridge design makes it easy to add more media if necessary or to remove carbon completely when medicating fish. The extra large size fits the TetraTec PF500 Power Filters.