Zilla Aquatic Reptile Internal Filter Size:One Size Above top and side mesh Above top and side mesh zippered entrances Belly wrap with buckle closure Measurements: XX Small: 8" 10" X Small: 10" 12" Small: 12" 14" Medium: 15" 18" Large: 19" 23" X Large: 24" 27" Cleans Efficiently and Designed For Terrariums Containing Up To 20 Gallosn Of Water Wide Cartridge Provides Larger Surface Area For Trapping Debris Protective Grate Within The Water Return Prevents The Reptile From Climbing Into The Filter Includes A Filter Floss Cartridge To Provide Superior Filtration Suction Cups Secure Filter In Place Replacement Cartridge Size Is 20G (Medium)