The Dymax Filter Media Bag – Extra Fine-Small is a zip-type filtering bag made of washable and bleachable fine nylon mesh material with a noncorrosive plastic zipper which provides durability and flexibility for filtration applications
The extra fine mesh is suitable for fine filter media such as:

Dymax Clear mix

Fine coral sand

Ammonia removal resins

Phosphate removal resins

Great for other fine filter media like  Macropore, Purigen

Features:

Zip-type filter media bag

Durable plastic zipper

Washable and bleachable nylon material

Durable and stretchable

Safe to use in freshwater or saltwater aquariums