Perfect Replacement Cartridges: Size: 11.5 x 15.7cm. The PF-L Cartridges Are Only Suitable for Top Fin Silenstream PF20, PF30, PF40 and PF75 Power Filters. Fine Carbon Filtration: Contain 3 times more activated carbon than other cartridges. Fully absorb and filter impurities or damaging substances to deodorize the water and reduce unhealthy gases. Further Cleaning: The outer layer is made of soft cotton with high-density fiber. The multi-layer cotton traps debris or waste without sucking up your fish, keeping water crystal clear and fresh. Reliable Material: The carbon is well wrapped in permeable bags inside. No leakage of powders or contamination of water. And the evenly distributed cotton won't block the normal water flow. Easy to Use: Before use, rinse it with cool water to remove the outside dust, then put it completely into the filter chamber. Replace it every 2 to 4 weeks to maintain a healthy water environment. size: 11.5 x 15.7cm Material: Non-woven fabric + plastic colour: white Package Contents: 6 x PF-L Filter Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.