Fish release waste into the same environment they eat, breathe and live in, making an efficient filtration system critical to their long-term health and well-being. Choosing the best filter for your aquarium will depend on aquarium size, the types of fish you keep, your feeding habits, maintenance practices, and to some extent your personal preferences.
What are external Power Filters?
Also known as hang-on-back (HOB) or simply hand-on filters, these are the most popular filters for small to mid-size freshwater aquariums because of their reliable performance and convenient maintenance. As their name suggests, they hang on the back of the aquarium, and water is drawn or pushed into the filter chamber where it passes first through a replaceable carbon-filled fiber cartridge and then some type of permanent biological media before returning to the aquarium. The discharged water agitates the surface, thus oxygenating the water and provides circulation within the aquarium. Some HOB filters can be manually loaded with individual media for more specialized use. Cartridges should be rinsed as needed and changed monthly. Most hang-on filters must be primed by filling them with water before plugging them in.
What are Canister Filters?
Compared to HOBs, canister filters hold more media and offer the aquarist unlimited flexibility in terms of media options. They are typically used in mid-size to larger aquariums in both freshwater and saltwater applications. Canister filters are positioned below the aquarium, usually inside the cabinet stand. Water is drawn into the filter through an intake tube, passes through the media and is then pumped back to the aquarium via a return tube. A spray bar or directional jet is used to agitate the surface and provide current in the aquarium. Canister filters function best as mechanical filters and are ideal for large aquariums, those with fish that create a lot of waste or fish that like strong current.
What are Internal Power Filters?
These filters are placed inside the aquarium and are driven by an integrated pump. Open style filters attach to the aquarium glass by suction cups or hang on the rim using clips. Water is filtered through a standard HOB filter cartridge. Closed style internal filters pass water through mechanical, chemical, and biological media chambers before directing it back into the aquarium through a controllable directional nozzle.
What are Sump or Wet/Dry Filters?
These filters were initially developed for the marine hobby, but can be used in freshwater systems, as well. Placed below the aquarium, water is gravity fed from the aquarium down to mechanical filtration media, such as a fiber sock or other filter pad material, and into the first chamber of the sump. From there, water is distributed over biological media where carbon dioxide is released, and the water is oxygenated. Additional chambers can be used for heaters, chemical filtration media, protein skimmers (used in marine aquariums only), and/or other purposes, depending on the needs of the aquarium. After flowing through all the chambers, water is pumped back into the aquarium. There are many different variations of sump filtration systems, but the basic function is the same no matter the design.
What are Sponge Filters?
Sponge filters are placed on the bottom of the aquarium. Using an air pump, water is drawn into the sponge and ejected through an exhaust tube. Some mechanical filtration occurs, however, their main function is as a biological filter. Due to the high surface area in the sponge, they filter fairly large volumes of water relative to their physical size. While not often used in display aquariums, many breeders use them in nursery tanks because they will not trap baby fish and they support important microorganisms that serve as a first food for newly hatched fry.