Octopus hang-on protein skimmers come in a wide assortment of models and are a good value even for budget minded aquarists. Our two most popular models are the Octopus BH-100F hang on skimmer which we recommend for tanks up to 50 gallons and the BH-2000 for up to 75 gallons. One of the downsides to many hang-on protein skimmers and filters in a small tank is the pumps and associated plumbing hanging in the aquarium detracting from the view. With that in mind most of the Octopus hang-on protein skimmers we carry (with the exception of the BH-100SS) have the benefit of being designed with the pump either in the body of the protein skimmer or hanging below it. With these designs the only parts in the aquarium are a small surface skimming box intake and an outlet tube. This design also makes these hang-on protein skimmers easier to remove from the aquarium as well for cleaning.