AquaClear Filter Insert Foam performs mechanical filtration by trapping particles and debris as they pass through the insert. This unique foam, designed for use with AquaClear Power Filters, features optimal pore size for efficient mechanical and biological filtration.Traps particles and debris and enhances biological filtrationTailored fit prevents water bypass for optimalSafe for fresh and saltwater useSizing:Size 20: 5-20 gallon aquariumsSize 30: 10-30 gallon aquariumsSize 50: 20-50 gallon aquariumsSize 70: 40-70 gallon aquariumsSize 110: 60-110 gallon aquariums