Features: Improve the amount of water-soluble gases in feeding. It can cooperate with cylinder, external plug-in and upper filter to doing pre-fine filtration. The biochemical cotton has great effect of complete filtration without dead angle. Multi-layer sponge designs, which can be continuously cleaned. Movings the cylinder does not affect the water quality. All types of accessories are compatible and flexible to use. We will provide two extra sponges as replacements. Specifications: Material: Plastics+Sponge Size: As Shown As Picture Type: 3811, 3810, 3821, 3820, 3831, 3830-type Package Includes: 1set Aquarium Filter Device note: 1. Please allow 1-2cm errors due to manual measurement, make sure that you do not mind before you order. 2. Due to the differences between different monitors, the picture may not reflect the actual color of the item. 3. We will provide two extra sponges as replacements.