Aquaclear Foam Inserts, 3-Pack (12-Pack, 20-Gallon) 4 3-filter packs of foam aquarium filter inserts Ideally sized for cleaning 5 to 20 gallon aquariums Effectively removes particles and debris from aquarium water Prevents particulate waste from prematurely clogging other media in the filter Primarily a mechanical filtration media, our foam also provides powerful biological filtration as friendly bacteria eventually grow inside its pore structure