Review on Uxcell Aquarium Cartridge Replacement Filters by Rachel Cook

Simply buy it! They are on every fence in my aquariums. I only close one end with a cable tie. Adds an extra surface area for beneficial bacteria to colonize while adding the necessary biological filtration. Also adds a pre-filter to HOB or CANISTER filters. I bought a few extra ones to rotate during water changes. Clean with tank water, not tap water. Highly recommended!