There are several methods used to filter marine aquarium water, and depending on the type of tank you have, you may want to select one or more of the following types of aquarium filters for your tank. The choices can be confusing, so we've put together this quick primer to help you decide How to Pick the Best Filter for a Saltwater Aquarium.
Built In Filters:
Many self contained nano aquariums on the market today come with a built in filter for saltwater or nano reef systems. Typically, this will be a smaller tank with a divider panel separating the back section of the tank from the front section, and makes use of an over flow and return pump built into the back filter section. You can add small live rock pieces, bio balls or other filter media to the back section, along with filter pads and carbon or other filtration media. There is usually also a section in the back filtration area for you to add a heater and a protein skimmer. A return pump comes with the system and keeps the water circulating from the built in filter section, to the main tank, and through the over flow chamber.
Protein skimmers are used to removed dissolved organic waste from the water. Typically the process involves a water pump sucking in water and mixing it with air to create a turbid water column with fine bubbles. The bubbles are fed up through a cylandar or cone shape, where they dissipate into larger bubbles that form a thin membrane of the organic waste. The larger bubbles over flow into a collection cup at the top of the cone, and condense into a thick, green muck that is the concentrated organic waste. The collection cup should be emptied as needed. Protein skimmers are recommended for reef systems, and for aquariums where a media reactor is being used for nitrate and / or phosphate control.
A media reactor can be used for specific filtration needs, such as nitrate or phosphate control. This is usually a long acrylic column that is filled with a filtration media, through which water is passed, then returned to the system by the use of a pump. Types of media include GFO (granular ferric oxide), or aluminum pellets for phosphate control, bio-pellets for nitrate and phosphate control, and carbon. The flow rate of the pump is determined by the type of media being used in the reactor. GFO should have a slow flow rate, where carbon and bio pellets perform better with a moderate to vigorous flow rate. The water flows through the reactor media and back into the sump.
Sumps, Wet / Dry Filters, and Refugiums:
These are generally considered to be primary filters for most saltwater and reef aquarium systems. They are basically all the same thing with some slight differences. All of these require the use of an overflow chamber and drain pipe. The water from the main tank flows downward into the sump, which is usually in the cabinet below the aquarium. A return pump is used to circulated the water back to the main tank. A wet / dry filter uses a felt filter sock for large particles and bio media such as filter pads and bio-balls and is generally suitable for marine fish only aquariums. A sump is a more advanced wet / dry filter, which typically uses live rock as opposed to bio balls, and has special compartments for heaters, filter media such as carbon, media reactors, and protein skimmers. Sumps are generally employed in reef aquarium systems with live coral. A refugium is a modified sump that has a central area that is used for reef mud substrate and growing a macro algae such as chaetomorpha. There is a light over the refugium to help the algae grow, which provides a refuge for micro fauna such as mini brittle stars, copepods, bristleworms and other critters that help to emulate the conditions found naturally on reefs.
External canister filters are usually used for aquariums that don't have overflows and sumps. A siphon hose draws water from the aquarium into the canister filter, where the water is passed through several stages of filtration, then returned to the main tank with a built in pump and a return hose. More advanced canister filters have built in thermometers, heaters, ultraviolet sterilizers and some even 'breathe' emulating the effects of a wet / dry filter. Most canister filters are suitable for fish only marine aquariums and for freshwater aquariums.
Hang On Filters:
Hang on filters are fairly inexpensive and simple filters, which are generally used for saltwater quarantine tanks or for freshwater aquariums. It is a plastic device that hangs on the side of the aquarium, it has a built in pump, and it pulls water from the tank and passes it through carbon and some sort of bio media such as a bio-wheel.
UV Sterilizers, Ozone Generators and Beyond:
UV Sterilizers are used to kill algae, bacteria and protozoa by passing the water through a shielded column that exposes the water to ultraviolet rays. Ozone Generators are used to eliminate dissolved organics from the water. Both are fairly advanced filtration methods, but are considered to be be very effective. Other types of new filtration method are being experimented with constantly all with the goal of creating the perfect water conditions for a happy and healthy aquarium!