There are several types of fish tank filters one can choose from that will match appropriately the size of the tank. Each of these type perform mechanical, chemical, biological filtration, or a combination of two or all of these functions. For small tanks, there are the hang-on filters, internal power filters, box or corner filters, diatom filters, and sponge filters. All these are of the inexpensive variety but have some downsides. Hang-on and internal power filters can perform all filter functions but has only a small surface area for filter media. The box or corner filter, diatom filter, and sponge filter get clogged up easily and require frequent cleaning. These types are usually kept as secondary or back-up filters.   Larger aquariums need more powerful fish tank filters. Canister filters, undergravel filters, fluidized bed filters, and wet and dry filters are ideal for these tanks. However, these filters have more maintenance issues, may require additional equipment, and a more complex set up than the simple ones.