Ideal Replacement Cartridges: Size: 3.7" L x 2" W. ONLY Suitable for Top Fin BF5 Bettaflo Filters which perfectly match Desktop Aquariums with Element 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 wont 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. Note: The data are all measured manually, please allow 1-3cm error, due to the difference in light and display, there will be a certain color difference, the actual object received shall prevail.