Aquatic Life Media Non-Woven Filter Sock for Aquarium, 200-Micron 200 Micron non-woven polypropylene fibers effectively trap small organic particles. Micro-pore design allows sufficient water flow through the sock while effectively polishing the water. Heavy duty plastic ring design allows for easy suspension in sumps, refugiums and filter boxes. Aquatic Life filter socks are the ideal way to add micron filtration to many filters! Suitable for Saltwater & Freshwater use - always rinse socks well before use.