This is a brand new, boxed, Red Sea 225 Micron Thin Mesh Filter Bag (R42197).

It is a 10.5"/26cm long filter bag for Red Sea Reefer Aquariums and Max S Series Aquariums and, will also fit any standard 4"/10cm filter bag holder.

This 225 micron thin-mesh bag is for new setups and after heavy maintenance or whenever there is a lot of particulate matter in the water. It is also suitable as a holder for other mechanical or chemical filter media. The monofilament construction of this bag makes it easy to clean.

This mesh bag is being sold as it came as part of a package for an aquarium I purchase however, chosen to use a filter roller instead of socks.