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Comprehensive Guide to Reef, Saltwater, and Freshwater Systems
This article is our main filtration article and covers a great many topics, and it also links to a variety of other articles and videos that will help explain the various subjects. The article begins with recommendations for reef aquariums, saltwater fish-only aquariums, and freshwater aquarium filtration. The article then explains the theory behind filtration (mechanical, chemical & biological), and explains why you should use protein skimmers, canister filters, wavemakers, algae filtration, UV sterilizers, organic carbon dosing, and other equipment in specific situations.
Aquariums are small bodies of water with a higher density of organisms than natural environments, leading to the buildup of waste products to toxic levels. Filtration removes these unwanted compounds from the tank's water, making the environment more suitable for keeping corals, fish, invertebrates, and other life forms you may plan to add to your aquarium.
All aquariums require biological, mechanical, and chemical filtration. Each of these filtration types requires different methods for reef tanks, saltwater fish-only tanks, and freshwater tanks. Below is a general guide to help you decide which products you need for your aquarium.
Biological filtration removes nitrogen breakdown by-products from the water. These nitrogen compounds appear in the tank as a result of the animals added to the tank, the food that is added to the tank, the algae that die off, and the respiration and metabolism of the fish and invertebrates. Even though water quality is usually excellent when an aquarium is first started up, as soon as animals are added, it starts deteriorating quickly. Biological filtration counteracts these negative effects and removes any noxious compounds that may have been added to the water due to tank population, feeding the animals, biochemical activity, etc. Biological filtration is best done with live rock, live sand, or biological media.
Biological filtration has four goals:
Bacteria are used to eliminate ammonia and nitrite. Ammonia present in the water is broken down to nitrite by a form of bacteria called Nitrosomonas. These bacteria appear spontaneously, or their proliferation can be accelerated by adding a batch of seeded gravel or rock from another tank. Seeded gravel is gravel, or rock, that comes from an aquarium that has been running for a while and already has a great deal of bacterial life. Transferring some of the gravel (rock, coral pieces) also transfers bacteria. Ammonia tests should always show zero mg/l or ppm. Even small amounts are unacceptable in reef systems, as they will definitely harm fish and invertebrates alike.
Nitrite must also be removed. Nitrobacter species appear spontaneously in tanks and convert nitrite to nitrate, a less damaging compound. Should nitrite tests of the aquarium water show merely low levels of nitrite, this is still an indication that, somewhere in the aquarium or in the filters, the natural breakdown cycle has been, or is being, interfered with. The hobbyist should immediately determine the source of the interference and remedy the situation. This may entail cleaning all mechanical filters, ensuring that the gravel or substrate is clean and free of trapped detritus and other organic matter, removing dead or dying algae, checking the cleanliness of corner overflow boxes and/or surface skimming siphons, etc. The presence of nitrite may also suggest that you are feeding too much or that the tank is overloaded to the point that the filters can no longer efficiently handle the biological load. This should prompt the removal of livestock or an increase in filter capacity by adding biological filtration.
Nitrates are another problem altogether. Traditionally, nitrate has been regarded as a non-harmful compound. Such may be the case in fish-only tanks, but it is not so in today's living reef aquariums. Nitrate is definitely a pollutant and affects the well-being and appearance of corals and other invertebrates. More important to most aquarists. Elevated nitrate levels can lead to excessive algae growth.
For reef aquariums, using live rock and live sand are the best method of biological filtration. MarineandReef.com does not sell live rock or live sand. It's best to purchase these products locally.
How Does Live Rock Perform Biological Filtration?
Fish-only saltwater and freshwater tanks might use a mechanical aquarium filter for biological filtration, as many of these filters have a small area for additional biological filter media.
Mechanical filters, such as canister and power filters, are containers that usually have filter pads/media and often include biological filter media, such as a biological filter pad or bio balls. The mechanical filter pad traps waste, which needs to be periodically washed off. With some canister filters, such as the Nu-Clear Model 547 Canister Filter, all the media is biological. When using filters such as the Nu-Clear 547, you should use a mechanical filter in line before the biological filter. For freshwater or saltwater fish-only tanks over 100 gallons, you'll definitely want to use one or more Nu-Clear Canister Filters (and for tanks from 50 to 100 gallons, you might still want to use one). The Nu-Clear brand will require some plumbing knowledge to set up,, as it must be used with plumbed-through-the-bottom tanks or an over-the-back overflow box.
Algae filtration in the form of a refugium, macro algae reactor, or algae turf scrubber is a method of purifying aquarium water by growing algae. As mentioned earlier, high nitrate levels can lead to excessive algae growth. This is because algae uses nitrate as a fertilizer. The algae strips the nitrate from the water and incorporates it into its tissue as it grows. When algae grow in the main aquarium, it is very ugly and unwanted. Devices such as refugiums, macroalgae reactors, and turf scrubbers are designed to grow algae outside the main display so that the algae can remove nitrate from the water column while preserving the attractive, algae-free display we all like.
Organic carbon dosing is a form of bacterial filtration that removes nitrate from aquarium water. In a healthy, mature aquarium, enough natural bacteria will grow that Ammonia and Nitrite levels should remain stable at 0 ppm. This is not the case with Nitrate levels. The reason is that the bacteria that remove nitrate from the water cannot proliferate because they are running out of something they need. In most cases, what is missing is Organic Carbon. When the bacteria run out of organic carbon, they stop proliferating and stop removing Nitrate from the water. Organic carbon dosing is the process of adding the necessary organic carbon back into the aquarium so that the natural bacteria can continue removing nitrate.
It is important to note that Organic Carbon is not the same as the Activated Carbon used for chemical filtration. Activated Carbon is not in a form that the nitrate-reducing bacteria can use, so it does not help reduce nitrate.
Organic Carbon dosing can be done by daily liquid additions, such as Brightwell’s Reef BioFuel, or by using a media reactor with bio-pellets. Carbon dosing can work in freshwater aquariums, but it is far more common in saltwater and reef aquariums.
Chemical filtration is most commonly achieved using activated carbon. The carbon's micro-porous structure absorbs dissolved organics, chloramines, fish odors, toxic metals, toxic gases, and growth-inhibiting enzymes. We carry the Inland Seas, Marineland, and Acurel activated carbon.
Tips for using activated carbon:
Besides activated carbon, a wide variety of resins, minerals, and other media have been employed by aquarists to remove either specific ions, such as phosphate, or a wide range of largely unidentified substances from aquarium water. Two Little Fishies PhosBan can be used alone to remove phosphate, or in the Two Little Fishies PhosBan Reactor.
Boyds Chemi-Pure and Chemi-Pure Elite come pre-bagged inside the jar. All other products need to be bagged using one of the Acurel Media Bags. All bags have ties sewn into the top for easy closure.
The Poly-Bio-Marine Poly Filters are pads that absorb and adsorb contaminants and other toxic materials found in nature or added to fresh and salt water, with or without fish and invertebrates. Medication added to aquariums for the treatment of diseased fish will automatically be removed by the Poly Filter (after serving its intended purpose). The pads are placed in any filter where chemical filtration media is intended (generally after the larger sediment has been filtered out).
Mechanical Filtration is the removal of unwanted particulate matter from an aquarium by trapping it in a dedicated location, such as a filter pad, which must be cleaned periodically. The key to this is the cleaning. A mechanical filter is useless unless it is cleaned.
Mechanical filtration is recommended for all freshwater tanks and saltwater fish-only tanks. Because reef aquariums are very delicate and require cleaner water, we recommend using a protein skimmer, either alone or in addition to a mechanical filter. Protein skimmers are also recommended for use with saltwater fish-only tanks. They cannot be used with freshwater tanks because protein skimmers require saltwater.
Keep in mind that mechanical filtration:
Protein skimmers are not always listed as a method of mechanical filtration, but they are the best form of mechanical filtration for any saltwater reef or fish-only tank. The motion generated within the skimmer injects air bubbles into the aquarium water, forming a foam on which organic molecules collect. This foam is captured in the collection cup and disposed of before it breaks down into toxic ammonia and nitrite.
With a canister aquarium filter, water is pumped at moderate pressure through a filter media. Canister filters are especially useful in aquaria with large or numerous messy eaters that generate a lot of waste. For these filters to be effective, they must be frequently cleaned at least once a month.
Marineandreef.com carries Inland Seas Nu-Clear Canister Filters (professional/commercial grade) and Fluval, OASE, and Aqueon style filters (complete with self-priming and easy setup features).
Power filters typically hang on the back of the tank and are easier to maintain but offer lower performance. Roller filters are new technology using motorized fleece to automatically replace used filter material, removing waste before it decomposes.
None of the above-listed methods will remove solid wastes from the nooks and crannies of your aquarium. One of the easiest methods for cleaning these areas is to gravel vac the aquarium as part of your regular water change routine. Some people install wavemakers to improve the chance of catching solid wastes in the mechanical filter.
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