The main difference between HOB filters and Canister filters is the size. The Canister filters are available in a larger size and externally filtrating equipment. It covers more space externally. While on the other hand, the hang-on back filter is placed on the upper of the aquariums and covers less space. Due to the larger space of canister filters, it is more efficient and their filter media increase the filtration process and are perfect for larger aquariums. The HOB filters are suitable for home use and small aquariums.