Goldfish and Aquarium Board Articles
Aquarium Filters and Filter Media
By Jacob (JBC223456)

Water quality is key to success in the hobby of fish keeping. Your filter, along with partial water changes (PWCs), helps to keep your water from building up toxic levels of ammonia, nitrite, or other waste. It also filters out debris and promotes gas exchange. Good filtration, combined with regular partial water changes, is the key to keeping your fish healthy. To help you decide what type of filtration may work best for you, this article will discuss the three primary types of filter media, the basic types of filters, and last but not least filter maintenance.

Filters are important pieces of equipment in the hobby of fishkeeping. Fish (and the bacteria that break down debris) produce ammonia, which is toxic to fish. Debris from fish poop, uneaten food, etc also build up over time. The bacteria (e.g. Aeromonas) that break down debris are also potential pathogens that can make our fish sick. In the wild a large volume of water immediately dilutes the wastes fish produce. In an aquarium, the wastes have nowhere to go, so we aquarists use filters. Filters keep constant water circulation through the filter media, which filters out particles (mechanical filtration), converts ammonia to less toxic nitrate (biological filtration), and removes contaminants and organics (chemical filtration) from the water. Most filters also create water flow and surface agitation, which help to promote gas exchange between the water and the air and keep fish supplied with oxygen.

Contents
Types of Filtration Types of Filters
Which Filter is Best for My Tank?

 
 

Types of Filtration

There are three types of filter media: mechanical, chemical, and biological.

Mechanical Filtration:

Mechanical media such as a sponge, screen, or floss, traps free-floating particles (leftover fish food, fish waste, decaying plant matter, etc..) from the water. Water should flow through the mechanical filter media before it flows through the biological or chemical media. This will prevent debris from building up in the biological or chemical media.

Marineland Penguin filter pad
Photo by Jacob
Foam mechanical filter media
Photo by Ingrid
Mechanical polishing filter Media
Photo by GoldLenny

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Biological Filtration:

Biological filtration means to establish bacterial colonies that will help keep ammonia and nitrite low in your aquarium. In a newly set up aquarium, it generally takes at least a month to grow colonies of bacteria that convert ammonia (toxic) to nitrite (more toxic) and ultimately to nitrate (less toxic). This process is typically called cycling an aquarium. Once there are adequate bacterial colonies to immediately convert ammonia and nitrite as they are produced, both ammonia and nitrite should not be detectable in your water by test kits. Nitrate will continue to build up in an aquarium, and should be diluted by regular PWCs. Keeping the biofilter bacteria alive is critical to keeping your aquarium water from getting toxic.

Lava Rock Biomedia
Photo by Betty
Marineland Bio-Wheel
Photo by Jacob
Seachem Matrix Biomedia
Photo by Ingrid
Ceramic Biomedia
Photo by Marilynn
Bio-Balls
Photo by Marilynn

Biological filter media provides a home for these bacteria. The biofilter bacteria grow in colonies on surfaces; therefore, biological filter media should have plenty of surface area for the bacteria to colonize. In addition to surface area, biofilter bacteria need plenty of oxygen to grow and convert ammonia to nitrate. The rate at which an individual or colony of nitrifying bacteria can process ammonia and nitrite is limited by the amount of oxygen available in the water. The biological media on which they grow should not collect organic debris because the bacteria, that break down debris grow fast, and consume oxygen that the biofilter bacteria need to thrive. In a 24 hour period, a single nitrifying (biofilter) bacterium will double forming two bacteria, however, a single debris eating bacterium can double in population every 20 minutes. Debris will reduce the effectiveness of the biofilter bacteria and may result in a mini-cycle (seeing measurable levels of ammonia and/or nitrite).

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Chemical Filtration:

Chemical filtration is the process of removing dissolved organic compounds and contaminants from the water. There are many types of commercial chemical media than can be used in aquaria. For example, zeolite can be used to remove ammonia; Poly-Filter removes metals; Purigen, activated carbon and other products remove dissolved organics like tannins that stain the water yellow or brown and phenols that produce that fishy smell. You should read up on whatever chaemical media you choose and understand how it works and what it removes. Quite a few chemical media will remove medications from your water, so be sure to remove chemical media when treating the tank with water-based treatments. Some chemical media are affected by salt. For example, zeolite will release ammonia it adsorbed when exposed to salt. Carbon may also remove trace elements needed for plant growth. Chemical filtration occurs when water passes though the chemical media, so good water flow through the media is critical to its efficiency. To keep debris from clogging the chemical media, it should be placed on the clean side of your mechanical media. To keep water flowing freely through your chemical media, rinse it weekly in either discarded tank water or dechlorinated tap water.

Seachem Purigen
Photo by Marilynn
Activated Carbon
Photo by Jacob

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Types of Filters

The best filters have room for all three types of filter media and allow you to choose the arrangement of your separate mechanical, biological, and chemical media. Water should first flow through the mechanical media to remove particulates and then through the biological and chemical media. These types of filters give you the ability to change or clean your mechanical media without disrupting your biological media. Directing the water to flow through the mechanical media first prevents debris from reducing the efficiency of your biological or chemical filtration.

Filter maintenance: It is important to do regular maintenance on your filter to remove built up debris in the media, however you need to be careful to avoid disturbing your biofilter bacterial colonies. Never use chlorinated water to clean your biological media. Always use either dechlorinated tap water or discarded tank water. Tap water typically contains chloramines or chlorine that kill pathogens and make water safe to drink. Both chlorine and chloramines will kill your biofilter bacteria. If your filter has combined mechanical, biological and chemical media (typically carbon), you will want to use it as long as possible and rinse it in either discarded tank water or dechlorinated tank water at each partial water change. If it gets stopped up you can smack it against something to clear it. In these combined filter pads, you can remove the carbon and, replace it with fresh carbon as needed.

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Sponge Filters:

Sponge Filter, Photo from Goldfish UtopiaSponge Filters are small filter sponges that have an airline tube connection. They serve as combined biological and mechanical filtration. You hang or suction cup the sponge filter to the side of the aquarium, connect an air pump to the filter using airline tubing, turn on the air pump and that's it. A check valve is also recommended to prevent back siphoning of water into the air pump if you lose power. Sponge filters have several applications. They are good for fry tanks because you do not have to worry about fry being sucked into the filter. Sponge filters can hold a decent amount of beneficial bacteria. You can therefore keep a sponge filter in one of your cycled tanks and just pull it out and place it in a hospital or quarantine tank to cycle it. Sponge filters can be used for small aquariums. In my experience, a sponge filter would be good for an aquarium of 15 gallons max. A sponge filter can also be used on the intakes of some types of powerheads for added biological and mechanical filtration.

Maintenance: Sponges should be cleaned in either dechlorinated tap water or discarded tank water with each PWC to remove debris. To clean the sponges in the tank water after a PWC, just give them a swish in the discarded tank water to remove any debris. After the filter has been in use for a while, you may have to smack the filter against something to clear it. Periodically, you should clean the tube with a filter brush. Only replace the sponge when it begins to fall apart.

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Internal Filters:

Internal filters are usually very compact, with mounting brackets and/or suction cups to mount the filter on the inside of the aquarium. Water is drawn through the bottom of the filter, and then passes through the filter media and then through carbon. These filters may come with pre-sized cartridges. After being drawn through the media, the filtered water will return to the aquarium through the top of the internal filter output. The disadvantage to internal filters is they take up space in the aquarium. They are typically small and use mechanical media for both mechanical and biological filtration, which means the biological media is less effective, and you may see ammonia and nitrite when you change the filter media. Internal filters are typically only used for small aquaria.

Maintenance: The filter pad or cartridge should be rinsed in either dechlorinated tap water or discarded tank water at each PWC. After the filter has been in use for a while, you may have to smack the filter against something to clear it. You will want to use the same filter pad for as long as possible because that is where many of your biofilter bacteria live.

Internal box filters are typically a small acrylic box that sits at the bottom of the aquarium. They use an air pump to move water through the filter media. A check valve should be used to prevent back siphoning of water into the air pump. The filter media in a box filter should be arranged so that water flows through mechanical media (e.g. filter floss) prior to flowing through biological or chemical media. Box filters should only be used for an aquarium up to 15-20 gallons.

Maintenance: The filter floss should be changed when it is dirty or rinsed in either dechlorinated tap water or discarded tank water and reused. Biological media can be rinsed in either dechlorinated tap water or discarded tank water when you see debris in it and chemical media can be replaced as needed.

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Undergravel Filters (UGFs):

Undergravel filters are grate-like filters that are placed at the bottom of the aquarium under the gravel. These filters must not be used with sand substrates. It is also advised not to have a UGF while trying to grow live plants, as the plant's roots will grow, and clog up the grates as well. UGFs have small slits in them for the water to pass through and tubes on each end for the placement of equipment to circulate the water. There are two ways to power a UGF. You can use an air pump with an airstone at the bottom of each tube which sucks water down through the gravel and then up the tubes. A check valve should be used to prevent back siphoning of water into the air pump. The best way to power an UGF is to use a powerhead or HOB filter to move water through the UGF and gravel. Both methods draw water up through the tubes, which causes water and debris to be sucked down into the gravel bed. The gravel serves as both mechanical and biological filtration. Undergravel filters have plenty of surface area for biofilter bacteria, but to work efficiently, they must be kept clean by vacuuming the gravel well during weekly PWCs. If too much debris builds up, it can result in anaerobic areas (stagnant areas in the gravel) and may result in the production of hydrogen sulfide gas, which is toxic and smells like rotten eggs. UGFs are usually used in conjunction with other types of filters for debris removal. You can also run your UGF in reverse mode. Instead of sucking water up through the tubes, you can attach a powerhead with a prefilter to each tube to push water down the tubes, reversing the water flow. The reverse flow blows the debris that settle to the bottom, up into the water column where your other filter(s) can then remove them. This method keeps debris from building up in the gravel and results in more effective biological filtration. Reverse undergravel filtration is best combined with other filters to remove the particulates.

Undergravel Filter
Photo by Betty
Undergravel Filter
Photo by Paula
Undergravel Filter
Photo by Betty

Maintenance: The gravel should be vacuumed thoroughly at each PWC. You may also need to remove the UGF annually to clean under it (Before doing so, move the fish to another container in their tank water).

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Powerheads:

Penguin Powerhead, Picture by BettyPowerheads are simple filters that hang inside your aquarium and move water. They usually come with some type of mounting system, like a bracket and/or suction cups. Some powerheads have a venturi--an air intake tube to incorporate oxygen with the water. This feature, and the fact that they can be aimed to increase surface agitation, make them very good at promoting gas exchange between air and water. Some powerheads include a sponge filter (or other media) on the intake, for biological and/or mechanical filtration.

Maintenance: Sponges should be cleaned in either dechlorinated tap water or discarded tank water with each PWC to remove debris. After the filter has been in use for a while, you may have to smack the filter against something to clear it. You should also disassemble and clean the impellor and impellor housing regularly.

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Hang on the Back (HOB) or Hang on the Tank (HOT) Filters:

HOB/HOT filters hang on the back of the tank. These filters come in various sizes ranging for aquaria from 5 gallons to 60 gallons. They draw water from the tank through an intake tube with a strainer attached to the end up into the filter, and then the water flows back into the tank via an overflow which creates a pleasing waterfall sound and helps to promote gas exchange between the air and water. The intake tube is usually adjustable, so it can be changed to fit the depth/height of your tank. There are many different types of HOB filters. Most combine mechanical, biological and chemical media into one filter pad, which is not optimal, and have little room for extra biological or chemical media on the clean side of the mechanical filter. Many manufacturers also recommend changing your filter pads often, which is very bad advice since you would be throwing away your seasoned biomedia.

Penguin 100 Bio-Wheel Filter, Photo by JacobEmperor Bio-Wheel Filter, Photo from Goldfish UtopiaSome filters like the Penguin or Emperor filters by Marineland incorporate Bio-Wheels into their design. Bio-Wheels are very good biological media as they are exposed to lots of oxygen from the air and have lots of surface area for the biofilter bacteria to colonize. However, over time they may not spin well and can stop totally. Penguins and Emperor filters also do not have room for other biological or chemical media on the clean side of the mechanical filter pad.

Aquaclear HOB filters are an example of a well-designed HOB filter. They come with a sponge mechanical media that is easy to clean and lasts a long time. They also have plenty of room for biological and chemical media. You can make even more room for biomedia by cutting the sponge in half lengthwise, so it's half as tall. The intake strainer is the only downside to the Aquaclear filters. The intake strainer tends to become clogged and reduce water flow, especially in planted tanks. This can be fixed easily by adding a different intake strainer with more surface area.

Maintenance: The filter pad or cartridge should be rinsed in either dechlorinated tap water or discarded tank water at each partial water change. After the filter has been in use for a while, you may have to smack the filter against something to clear it. You will want to use the same filter pad for as long as possible because that is where many of your biofilter bacteria live. You should also disassemble and clean the impellor and impellor housing regularly. Keep the bearings clean on your Bio-Wheel. The Bio-Wheel can be gently rinsed with either dechlorinated tap water or discarded tank water. Since the Aquaclear filters have separate mechanical and biomedia, and if the biomedia is well colonized with bacteria, you can clean your aquaclear filter sponge more aggressively at each partial water change.

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External Canister Filters:

External canister filters are sealed filters that are placed outside the aquarium, typically out of sight under the aquarium stand. They have an intake tube that draws water from the aquarium into the filter where it flows through various media, and a return tube/hose to return water to the aquarium. One benefit of this setup is that you can control the direction of the water flow in the tank. Another is that the unsightly filter is not hanging on the tank or inside of the tank. These filters are great, because they have plenty of room for separate mechanical, biological and chemical media. The mechanical media should be arranged inside the filter so that the water flows through it first. External canister filters require the most assembly of all of the filters mentioned here. The only two parts of this type of filter that are placed inside of the aquarium are the intake tube and output tube/spray bar. After you assemble this type of filter, you will have to prime the filter (which means to fill it up with water). The intake tube should be under the water, and a priming mechanism is used to start siphoning water into the filter. Once the filter is filled, it is turned on for use. Since these are the largest filters, they are the most expensive (but definitely worth the cost). These filters are used for larger aquariums, ranging in size from 30 gallons all the way up to 200 gallons.

Rena Filstar XP1 Canister Filter
Photo by GoldLenny
Fluval 404 Canister Filter
Photo by Ingrid

Maintenance: Mechanical sponges or pads should be cleaned regularly. The time in between cleanings of the mechanical sponges or pads varies based on the fish load, the bioload they produce, and the amount of food you feed them. Every few weeks is typically adequate, but for a heavy bioloads more frequent cleaning may be necessary. If you notice that the flow is reduced on your canister filter, you should clean the mechanical media and the impellor more frequently. This typically involves either cleaning the mechanical media or replacing it. It also involves using a filter brush to clean out the impellor. Only replace the biological and/or mechanical media when they begin to fall apart. Biological media can be rinsed in either dechlorinated tap water or discarded tank water. Chemical media is replaced as needed. If your canister filter is making a lot of noise, it could be due to air in the filter or not enough water in the filter. If there are air bubbles in your filter after it has been primed and plugged in, usually this will go away on its own, but sometimes a rocking it gently while it is still running will get rid of those bubbles. If your filter does not have enough water in it, unplug the filter and prime it to fill it with water before turning it on again.

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Sump Filters:

A sump is a separate container (e.g. an aquarium, Rubbermaid tub, etc) that typically sits under the tank. Sumps are used for larger aquaria. They can be bought pre-made with filters already in place and with Bio-Wheels or they can be homemade. The benefits of a sump include adding extra water volume to the system, room for larger filters and the ability to place your other equipment like heaters out of sight in the sump. Typically, water flows out of the main tank via an overflow and down into the sump. The water then passes through mechanical filter media and then trickles down over biological media. This is very efficient filtration because you can change out or clean the mechanical media without disrupting your biofilter bacteria and there is plenty of room for biomedia. Since the water trickles down over the biomedia, there is lots of oxygen available for the biofilter bacteria to use. There is also plenty of room for added chemical media as well. A pump sits in the bottom of the sump and pushes water up through tubing or a hose back into the aquarium. The flow of water between the tank and the sump must be balanced and there must be enough room in the sump for any water that would flow out of the aquarium during a power outage.

Overflow
Photo by Betty
DIY Trickle Tower Filter
Photo by Betty
Return Pump and Plumbing
Photo by Betty

Maintenance: This typically involves either cleaning the mechanical media or replacing it. Biological media can be rinsed in either dechlorinated tap water or discarded tank water. Chemical media is replaced as needed. You should also disassemble and clean the pump impellor and impellor housing regularly.

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Which Filter is Best for My Tank?

In general, it is best to choose a filter with separate mechanical media and room for biological and chemical media in an area where water has first passed through the mechanical media. That way your biological and chemical media stays relatively free of debris and you can clean or replace your mechanical media without disrupting your biofilter bacteria. For certain applications like raising fry, shrimp or other small creatures that could get sucked into a filter, a sponge filter may be best, though HOB and canister filter intakes can be covered with a sponge or filter media to keep small creatures from being sucked into the filter. Undergravel filters can also be useful in small tanks, but must be vacuumed regularly and kept clean. For medium sized tanks, a good HOB and/or canister filter should be fine. For larger tanks, multiple HOBs, canister filters or a sump may be the way to go. If you plan to keep goldfish or turtles, you will need filters with separate mechanical filtration that optimally move 10 times the gallons in the tank per hour, however, if you use a canister filter, because of the increased amount of biomedia, you can get by with a lower flow rate. If you plan to keep tropical fish, you will need a filter that will optimally move 5 times the gallons in the tank per hour.

Regardless of which filter you choose, regular filter maintenance is the key to keeping your filter working efficiently. Even with a good filter, you will need to perform regular PWCs that include vacuuming your substrate. PWCs reduce nitrates, other organics, potential bacterial pathogens, and pheromones that accumulate in your aquarium, and they replenish the buffers that keep your pH from slipping down over time. Maintaining good water quality is the most important thing you can do to keep your aquatic creatures healthy and happy.

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References

A version of this article was originally posted on Tropical Tank Forum and Canadian Fish Forums. Content from those articles was included by the original author (JBC223456), with the permission of the administration on both sites.

Thanks to Dataguru (Betty), liv, Ingrid and Becky for additions and information included into this article.