Filtration FAQ

Can I use an undergravel filter with sand? Do I need to put somthing between the filter and sand bed and what should I use?

You cannot use an undergravel filter with sand as the sand will pack down too tightly to allow water to flow properly through the substrate.

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Would it be a good idea to use both a hanging filter that uses carbon and an under gravel filter in a 10 gallon aquarium?

Absolutely! In fact, this is the best way to filter small freshwater aquariums.

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What are the three basic types of aquarium filtration?

The three basic types of filtration used in aquariums are biological, chemical and mechanical filters.
Biological Filtration uses nature to keep your aquarium clean. There are two types of biological filtration. These two types are known as aerobic (nitrifying) filtration and anaerobic (de-nitrifying) filtration. Both of these types of filters work by cultivating bacteria or algae which convert the toxic nitrogenous waste of aquatic animals into less harmful nitrogen compounds. These compounds may be gases that naturally escape into the air or liquids that can be removed by doing periodic partial water changes. Examples of aerobic biological filters you can buy are under gravel filters, wet/dry or trickle filters, and fluidized bed filters. There are several types of anaerobic, de-nitrifying filters you can purchase. We recommend that aquarists who want to try a denitrifying filter read up on the subject and proceed cautiously. Some anaerobic filters, if not used carefully, can do more harm than good if added to an already-established aquarium.
Chemical Filtration uses activated carbon, or other chemical media (such as ion exchange resins) to purify aquarium water. The carbon or other material removes toxins and impurities as water passes through the filter. A chemical filter will remove toxins and solid waste from aquariums that are not removed by a biological filter. Most chemical filters are hanging power filters and canister filters. Hanging power filters are typically used on aquariums under 35 gallons, and canister filters are used on larger aquariums.
Mechanical Filtration removes particles from the aquarium that may discolor or cloud the water by passing the water through a fine floss or mesh material. Mechanical filters remove particles that may clog the biological filter in an aquarium. Most chemical filters are also mechanical filters. Many aquarium hobbyists use both a biological and a separate mechanical/chemical filter. Using two separate filters helps keep an aquarium clean in between water changes, and also provides a "back up" in case one of the filters stops running. There are several good arguments against using mechanical/chemical filters in certain types of aquaria, such as live-reef tanks, where they may remove valuable nutrients or food microorganisms from the aquarium.

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Are under gravel filters obsolete?

Certainly not! Under gravel filtration will always be available for those hobbyists who want a good, low-cost biological filter for their freshwater or smaller, under-stocked marine aquariums. Wet/dry or "trickle filters" are a vast improvement in biological filtration compared to under gravel filters. However, most well-made wet/dry models are considerably more expensive than an under gravel system. Under gravel filters still play an important role for freshwater enthusiasts and marine aquarists on a tight budget.
If you are setting up a serious marine aquarium, especially a reef tank, we strongly recommend the use of either the Berlin or Jaubert methods, or a wet/dry filter/protein skimmer combination, as opposed to an under gravel filter. However, if you are setting up a freshwater aquarium, or a very small marine aquarium (which we frown on), an under gravel filter still remains a viable alternative if budget is a concern, and in the case of marine tanks, if the tank is under-stocked.
For most of our marine aquarium clients, we have set up systems with either a wet/dry filter and protein skimmer or a Berlin tank. Depending on the client's wishes, the biological load in these tanks, and other factors, we may also use canister and other filtration methods to supplement or enhance the primary biological system. We also have several clients for which we have set up systems based on Lee Chin Eng's original system from the 1960s to early 1970s, which uses great lighting, good aeration and water flow, combined with a low fish population, but uses no commercial filtration at all!
Yet we do have several clients who still use under gravel filtration systems as the primary filtration method for their small to mid-sized saltwater aquariums, and even one or two who use under gravel filters in their reef tanks. These aquariums all have four things in common: They are under-stocked, having fewer fish than are kept by most of our other clients. They are all equipped with excellent water flow and aeration. They all have a certain amount of live rock as part of the decoration scheme. Finally, they have all been relatively successful. It is very difficult to try to sell someone on the idea of up-grading their aquarium with modern filtration when they aren't experiencing any major problems with what they already own! The bottom line is you should first do some reading, decide in advance which animals you want to keep, and then design a filtration plan that suits their needs.

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What is a Berlin System?

Let us start by stating that the Berlin method will only work well with saltwater marine reef aquariums, as it is totally dependant on the use of live rock and the lighting systems used to support a living-reef closed aquatic ecosystem. Each year, more and more live-reef aquarium enthusiasts are setting up new tanks or converting existing aquariums to the Berlin method of filtration. The Berlin method was discovered by hobbyists in Germany (surprise!), hence the source of the name. It works on the concept that all of the microorganisms necessary to support a marine reef aquarium can be found in and on live rock collected from the ocean. This includes aerobic, facultative anaerobic, and purely-anaerobic bacteria, many other microorganisms, algae, and filter-feeding sessile invertebrates. The only commercial filtration used is a high-quality protein skimmer.
Most live rock are pieces of coral reef that break off as a result of storms and strong wave action where it collects in relatively shallow waters. There is also commercially-cultivated live rock available, produced by "seeding" coastal waters with mined rock, which is quickly inhabited by desirable reef flora and fauna.
The Berlin method is quite simple and deserves a simple explanation. It is basically a reef aquarium with a fair amount of live rock, equipped with good lighting, an empty wet/dry filter or reservoir (USING NO FILTRATION MEDIA), good water circulation, and a protein skimmer. As in most reef tanks, a chiller is usually used to maintain the correct temperature.
Bacterial populations in and on the live rock remove all nitrogenous waste. The absence of a large, external bacterial population (as in a wet/dry filter), allows the nitrogen cycle to proceed at a slower pace, letting anaerobic bacteria complete the cycle by converting nitrate to nitrogen gases. This virtually eliminates nitrates from the aquarium! The skimmer is there to remove all dissolved and solid organics not processed by the bacterial populations in and on the live rock. The reservoir, also called a "sump", is located under the aquarium, and is fed by water drawn from the surface of the display tank via some form of overflow or prefilter, the same as that used for a wet/dry filter. The difference is that no filtration material is used. The reservoir is equipped with a large, efficient protein skimmer. A pump delivers water back to aquarium, and additional pumps may also be used to provide good flow around and through the live rock structure. As mentioned, a chiller may be necessary to maintain proper temperature. The live rock used to construct the reef should be set up with spaces in-between individual pieces of rock to allow good water circulation to penetrate through the reef construct.
This system is proving to be one of the best for supporting marine reef tanks. If set up and maintained properly, the aquarium will remain extremely healthy, exhibiting little or no nitrates and phosphates. It will be a thing of beauty, and has the added bonus of requiring less maintenance and water changes than other methods require . . . but there is one major catch: In order for this type of aquarium to be successful, patience must be exercised in stocking the reef with animal life. It may take up to between six months to a year to complete the display, and no fish at all should be added until the reef is almost complete. Because the nitrogen cycle proceeds on a slower scale than in an aquarium using conventional biological filtration, great care must be taken not to exceed the nitrogen-handling capability of the bacteria populations with each addition of livestock. Stocking a reef aquarium slowly is good practice anyway, so we highly recommend the Berlin method.

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How do Wet-Dry (Trickle) filters work, and which type should I buy?

Wet-dry filters, also sometimes called trickle filters, are biological filters. The basic design and mechanics of most trickle filters is roughly the same. Water is drawn from the surface of the aquarium, is first pre-filtered, and is then delivered to the filter material in a manner that allows the water to trickle through the material in a chamber. Some designs use drip plates above the main filter material chamber to produce this "trickle" effect. Others use spinning or stationary spray bars to deliver water to the filter material.
Beneficial bacteria cultivate in the filter material and remove harmful ammonia and nitrite from the water. The filter material used in these filters can vary greatly in design, but usually has a high surface area so as to allow more room for greater bacteria populations.
The filter material is usually suspended several inches above the bottom of the filter. This allows water to collect below the filter material in a reservoir or "sump." A pump then delivers the water back to the aquarium where the whole process repeats itself.
In some wet-dry designs, there is a space or separate chamber in the reservoir where additional filter material or chemical media may be kept fully submerged or "wet." The main filter material is kept damp ("dry") by the trickle action of the aquarium water. This is the origin of the term "wet-dry" to describe this filtration method. Wet-dry filters were invented to overcome some of the limitations of under gravel filters, especially for saltwater aquariums.
Unlike an under gravel filter, most of the filter material is not fully submerged in a wet-dry filter, so there is unlimited oxygen available to the aerobic bacteria that live in the material. The trickling action of the water through the material also helps to aerate the water thoroughly. Finally, the beneficial bacteria in the filter are not in direct competition for oxygen with the fish in the aquarium. There are two basic designs of wet-dry filters on the market. The normal wet-dry filter has a separate pre-filter box that hangs on the aquarium back which delivers water to a larger, wet-dry filter chamber that sits below the aquarium. Aquariums may also be pre-fabricated with a built-in prefilter inside the tank (sometimes called "reef-ready") for wet-dry filtration.
There is also a hang-on version of the wet-dry filter, for situations where space is limited under the aquarium. This design is a completely self-contained system, and the entire filter hangs on the back of the tank. These are often called "reef-conversion" filters. In many of these designs, the filter material is half-submerged. Some so-called "integrated" aquariums actually have a version of this filter built into the back of the aquarium.
If space is not an issue, we recommend purchasing a true wet-dry filter with separate components, rather than an integrated hang-on-the-tank model. They are larger, easier to service, more efficient, and it is simple to add a protein skimmer to this design. Some of the hang-on "reef-conversion" filters may have integrated protein skimmers built-in, but these skimmers are not easy to adjust and are usually not as efficient as those designed to be separate components.

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I have a saltwater aquarium. Do I really need a protein skimmer?

Most definitely! It is our opinion that the protein skimmer is the most valuable filtration device available to marine aquarium hobbyists.
If you've ever seen foam or oils on the surface of the water in your tank, you've seen some of the deadlier, oxygen robbing organics that a skimmer can remove. These oils, lipids, and proteins are broken down by bacteria which produce toxins as a by-product of their metabolism. It is still theorized by many aquarium gurus that this process was and still is responsible for the mysterious "wipe-outs" that occur much less-frequently now that protein skimmers are in wide use throughout the hobby.
Protein skimmers use a process called foam fractionation to remove many dissolved and solid organics from the water. In most skimmer designs, a large diameter contact chamber forms the base and main body and narrows gradually in diameter near the top. It is equipped with an inlet at the top and an outlet near the bottom. There is also always a method of delivering a powerful flow of very fine air bubbles to the contact chamber. Attached to top of the contact chamber is a narrow clear fractionation chamber. Surrounding and rising above the top of the fractionation chamber is usually a clear waste collection chamber which can be removed for cleaning.
Water that has been drawn from the surface of the aquarium and tons of air bubbles enter the top of the contact chamber at high velocity. The water travels down the chamber as it is saturated by the air bubbles. Organics in the water coat the bubbles which rise up into the fractionation chamber. Here the oil-coated bubbles concentrate, foaming themselves eventually into a pasty brown bubbly froth that rises and falls until it eventually spills over into the collection cup.
Once you've seen what a protein skimmer removes, you'll wonder how your saltwater aquarium did without one. If your present marine aquarium will accommodate one - add one. If you're setting up a new saltwater tank, don't do without one! Because of the lower density of freshwater, protein skimmers do not work nearly as well for freshwater aquatic systems unless it is a high population and/or dissolved-organic load situation such as a large fry-raising tank, an outdoor pond, or a fish farm.

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What is a plenum and how do I create one in my tank?

The plenum method was discovered by Dr. Jean Jaubert and is often referred to as the Jaubert System. "Plenum" refers to an un-oxygenated layer of water trapped beneath a deep layer of gravel or sand at the bottom of an aquarium. This layer of water becomes anaerobic. Bacteria cultivate in this oxygen-free environment and remove nitrates from the aquarium.
There are several variations of the plenum, depending on what literature you read. The basic structure of the plenum system is essentially a relatively deep (3" to 4") layer of gravel, suspended 2" to 3" above the bottom of an aquarium. It is usually recommended that very little or no water flow should be directed across the gravel surface. A basic plenum may be created by suspending egg crate material or under gravel filter plates above the aquarium bottom, using inert supports such as PVC pipe. If egg crate is used, it is covered with nylon screening over which the deep gravel bed is placed. The actual materials, including what grade of gravel or sand is used, vary depending on what literature you read, but usually coarse live sand, fine coral gravel, or a combination of both are used. One technique is to use 2" of live sand on the bottom, over which nylon screening is placed. The screen is then covered by 2" of fine coral gravel. This allows the aquarist to turn over the top inch of gravel occasionally to clean it, without disturbing the anaerobic layer below.
Anaerobic bacteria form in the bottom depths of the substrate and in the water below. As anaerobic bacteria cultivate, they remove nitrates. Anaerobic action produces a fair amount of heat. The heat warms the water layer below the gravel. The warmer water flows upwards, displacing cooler water above the gravel. This action moves water through the plenum at very slow rates. The slow movement of water through the gravel helps to prevent dangerous hydrogen-sulfide gases from forming in the plenum. The deep gravel bed also provides a home for burrowing motile invertebrates which feed on solid organic mulm and detritus. These burrowing animals, which are either purchased and/or cultivated on their own from live rock, serve to keep the plenum porous and aid in the slow movement of water through the system. "Burrowing" sea cucumbers that serve this function well may be purchased from a good aquarium store.
The aquarium is stocked with live rock, but not as much as is typically used. The live rock construct should be suspended above the gravel bed, allowing water to move freely beneath the reef. This may be accomplished in a number of ways. One way is to place a couple of "anchor" pieces on the gravel bed, and glue others to the back of the tank using aquarium epoxy putty (not silicone!). The rest of the live rock may then be bridged across these supports to build the reef, but not too high. The construct should be loose, not tightly packed together, to allow good flow through the rock. Care should be taken, however, not to direct flow from pump returns across the gravel. The emphasis in aquariums using a plenum should be on the reef, with a minimal number of fish to balance the ecology.
The Jaubert System, if constructed properly, can work well, provided the aquarium is only lightly-stocked with fish. While we are sure some hobbyists would disagree with us here, we feel that more research is necessary on this fascinating subject. The original plenum method used aeration as the only means of water movement in the tank. We highly recommend that a plenum be used in conjunction with a Berlin system. The protein skimmer will remove other dissolved and solid organics, not removed by the plenum. The use of a protein skimmer combined with the plenum method may be the key to keeping more fish while using this type of biological filtration.
If you're setting up a new aquarium, installing a plenum will be relatively easy. If you have an existing reef tank, installing a plenum will involve a fair to major amount of work. Definitely read up on the subject before you go to work.

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How does biological filtration work?

In an aerobic biological filter, oxygen-rich water is passed through filter media by a pump. Oxygen-loving (aerobic) bacteria form on the filter material. These bacteria consume toxic fish waste (ammonia), making it harmless by converting it first to nitrites, and then to nitrates. Nitrates are the by-products of the metabolism of the bacteria. Low amounts of nitrates in aquarium water do not harm many fish, but can impede the growth and health of many live-reef corals and other invertebrates. High levels of nitrate in an aquarium will eventually harm all the animals in the aquarium. Nitrates are usually removed by partial water changes, or sometimes by the use of denitrifying filters.
An anaerobic biological filter requires an environment that is very oxygen-poor. Bacteria that flourish in the absence or near-absence of oxygen cultivate on filter media through which water moves very slowly (or in some cases, not at all). These bacteria consume nitrates and other nitrogenous waste in aquarium water and convert them into nitrogenous gases such as nitrous oxide, which leave the filter as bubbles that rise to the surface and escape into the air. Some of these filters cultivate bacteria which require feeding of a simple alcohol or sugar to do their work. Other types of de-nitrifying filters work by cultivating facultative anaerobic bacteria that can live in oxygen-rich or oxygen-poor environments and do not require additional feeding.
Aerobic (and anaerobic) biological filtration takes place in all well-established aquariums, even if the aquarium has no filters at all! There are biological filtration methods that use more natural means of cultivating beneficial bacteria, both aerobic and anaerobic, such as the "balanced" live-plant freshwater aquarium or the "Berlin" and "Jaubert" methods of keeping a living-reef aquarium. These methods usually do not use any additional filter media to cultivate beneficial bacteria other than the rock and gravel (or sand) in the aquarium.

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I have a wet/dry filter and a protein skimmer on my saltwater aquarium. Do I also need a canister filter?

The operative word here is "need." The purpose of a canister filter is two-fold. They are used to remove solid waste from the water column mechanically, and also to hold chemical adsorption or ion-exchange material. Canister filters are also invaluable for pre-filtering water before it passes through an ultraviolet sterilizer to increase kill-ratio by clearing the water for better light penetration. Pumps combined with canister modules can also be used to pre-filter water before it passes through a chiller to keep the internal plumbing of the chiller clean, thus aiding cooling efficiency.
One of the problems with using carbon, phosphate-removal media or other chemical filtration media in the sump of a wet/dry filter is that water passes through the path of least resistance. A bag of carbon in the reservoir will only have so much water passing through it as the water would "much rather" move around it or over it. A canister filter allows the chemical media to be placed in a sealed chamber so that water must pass through the media where it can be treated.
If you do regular partial water changes on your aquarium, and already have a protein skimmer, you may never "need" a canister filter. However, if you have a particulate or debris problem in the tank, discolored water (stop over-feeding and lower your fish population!), bacterial or algae blooms, or you want to install a UV sterilizer, you may want to consider getting a canister filter. Remember, however, that every pump you add to your system adds heat to the aquarium. If you have a chiller - no problem. If you don't, check your temperature and make sure you can add another filter before you buy.

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Frequent Aquarium Questions