The basic aquarium filtration systems include the chemical, biological, and mechanical filters. The variants of these filters include internal, external, and the under-gravel filtration systems.
The external filters are the best if you can afford around $150. The under-gravel is least desirable; however, you can Filters are categorized as chemical, biological, and mechanical. You can purchase external, internal, and under-gravel filtration systems to support your fish aquarium.
If you are just starting out in fish care and aquarium care, avoid the under-gravel filters since it will require excessive maintenance, as well as the filters do not produce quality power.