The Reef Octopus Classic 100-HOB Protein Skimmer is a favorite hang-on back skimmer. Capable of filtering aquariums up to 75 gallons, the Classic 100-HOB features an easy to install and operate design in which the pump is mounted inside the aquarium. To install, simply place the skimmer on the back of the aquarium, mount the pump in place, adjust the intake strainer and it's ready to skim. The Reef Octopus Classic 100-HOB is constructed of high-quality acrylic and equipped with a highly-efficient Aquatrance pinwheel pump, which produces an ideal mix of water and air for optimal waste removal. For aquariums up to: 105 gallons, light bio load; 75 gallons, medium bio load; 55 gallons, heavy bio load. Pump: Aquatrance 1000. Footprint: 8" X 3.75", 17" tall. Installation: Hang on back.