Aquarium protein skimmers are designed to hang on the back of the tank, sit in the sump, or sit in the tank. Some protein skimmers are designed for both in sump and hang on the tank use. All the protein skimmers for sale on this page are in sump protein skimmers. They range from very affordable protein skimmers for small tanks to AquaC, AquaEuro and Bashsea Protein Skimmers for tanks up to 300 gallons.