This filter media bag a re-useable bag that you can put activated carbon, Zeolite, Peat, Phosphate removing resins or any other loose filter-related media in. 

Buying these products in bulk will save you money and this bag will give you a place to keep the loose filtration products.

This product is safe for use in freshwater, ponds, and even Marine aquariums. 

The durable fabric and drawstrings will allow you to get continued use out of these bags.

The size (5"x3.5") is quite common among many filters.

This item ships from Canada :)