Biochemical filtration module: The figure is only a schematic effect, the actual filter element is not full in the dry state. The biochemical filter element has good water absorption, the state is dry when leaving the factory, the volume is small and rich in active holes, and it will absorb water and when placed in a fish tank with water. Expiration reminder: refers to the function of the fish tank as a whole, not the function of a single filter element. Suitable for fish farming: Nitrate is produced around the 12th day of using the filter element, and the nitrification system begins to be established. After 30 days, the nitrate is stable at around 20-40 mg/L, which is suitable for fish to live in for a long time. Made of High Quality Meterial, Stronger And More , Improve The Appearance Easy to use,Easy to replace Free water change for half a year: 10 tropical ornamental fish of 7-12cm, fed twice a week, water pump 3 gears, no death within 180 days, ammonia nitrogen content 0-0.2mg/L after 6 days, nitrite content 0-0.01mg/L after 11 days, nitrate stability range 20-40mg/L after 30 days, pH long-term stability between 6-7, test data from Laboratory of Painting Geometry. Colour:Gray Material:plastic Package Contents: 2 x Physical filtration module 1 x Biochemical filtration module 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.