The other one is Poly-Filter
It used to be made by a company called Underword, but it's now made by Arcadia. You'll still see some shops advertising it under the Underworld name.
It's not filter wool/filter floss but a filter medium that removes various substances.
Poly-Filter - Arcadia Aquatic
An established favourite from the U.S. the unique POLY-FILTER is now available once more through Arcadia. Poly-Filter is a real asset in the fight to achieve the best water quality and sparkling clarity in your aquarium. There are many chemical products that can build up in the aquarium water...
www.arcadia-aquatic.com
It used to be made by a company called Underword, but it's now made by Arcadia. You'll still see some shops advertising it under the Underworld name.
It's not filter wool/filter floss but a filter medium that removes various substances.