Fine Mesh Bag: Size: 7.9" L x 5.9" W; Hole diameter: 2 mm. Totally 6 white and 6 black bags. Nothing can pass through the net except water. Ideal for holding large aquarium filter media, such as activated carbon, bio balls, zeolite, crushed coral, etc. Robust Material: Well sewn with soft but strong polyester, the mesh bag is sturdy, wear-resistant and reusable. Dependable for long-term soaking in most aquariums or fish tanks Practical Zipper: The opening of the filter material bag is sealed by a top zipper. It always wraps the filter media inside without leaking out. Convenient to open or close the bag for easy replacement of materials Fit Multiple Filters: The aquarium filter media bags are suitable for diverse filters, such as canister filters, power filters, pond filtration systems, etc. Connect all the filter media together to keep your aquarium clean Safe & Reliable: The aquarium bag is washable and fade-resistant. No more worries about water contamination. Fish Tank Fine Mesh Bag with Plastic Zipper Aquarium Reusable Mesh Bag for Activated Carbon Bio Filter Balls Filter Stones