Aquarium Filters

Aquarium filtration is a key component of almost any aquarium ecosystem.  There are many different options to choose from and an almost endless number of variations possible.

Ideally, you want to create and maintain something as close to the natural environment as possible.  In a healthy natural ecosystem, there will typically be far less fish per gallon than in a fish tank and the water will constantly be naturally replenishing and filtering itself in many different ways.

In a home environment the concentration of fish will be greater and you have to use filtration and/or water changes to keep the water quality suitable to maintain aquatic life.

The core components of any filter system will be physical or mechanical filtration and biological filtration.  There are many different forms of both of these types of filtration methods and they can often be used together.  There are also various forms of chemical filtration and other methods such as UV sterilization or ozone that can be used as well although these should generally only be used secondarily, intermittently, or to address specific issues.

The most common form of physical filtration is water passing through a polyester fiber media at a fairly rapid rate.  Particulates and waste in the water become trapped in the media.  Bacteria can also form in this media as well and their growth will absorb contaminants and waste.  Usually these can be rinsed out at least 2 or more times and re-used.  Eventually, they should usually be completely replaced with fresh fibrous media.  Sometimes filter socks are used with dense fibrous media.  If it is very dense them beneficial microorganisms will not pass through.  Microfauna can still remain established in the aquarium especially if there is a sump area or a lot of rockwork or plants in the aquarium for them to live.  You can cut a small hole to the side of the filter sock to let some of the beneficial microfauna through while still filtering the majority of the water passing through.  Carbon is actually a form of physical filtration as small contaminants down to the molecular level will become trapped in the microscopic cracks of the carbon.  Protein skimmers are another form of physical filtration only available in saltwater aquariums.

A common form of chemical filtration would be the ammonia/nitrate removal products available.  These are good to keep on hand when initially cycling a tank but afterwards should only be used occasionally or perhaps to combat an ammonia spike caused by a dead fish that you couldn’t remove from the tank for some reason.  There are also resins and other media such as zeolite or phosphate remover that would qualify as chemical filtration but they should also be considered a secondary and minor form of filtration in the system.  They should not be relied upon as a primary method of maintaining an aquarium.

UV sterilizers will be covered in greater detail but ozone makers are similar.  UV sterilizers are far more common, safer, and affordable and serve the same function as ozone generators.  They will kill microorganisms in the aquarium and will not actually remove anything at all.  If used continuously they will sterilize the aquarium and remove beneficial microorganisms.  This might be necessary to combat an ich outbreak or other fish disease and might be the best available option to combat a cloudy tank or algae outbreak at times.  It is better to limit their use but are an important component to have handy when needed.

Another important function of the filtration system will be to circulate the water in the aquarium and aerate and oxygenate the aquarium.  This is true with power filters that include physical and fast flow biofiltration as well as protein skimmers.  However, other methods of water circulation and aeration should definitely be used as well.  This is because as the physical filter media becomes clogged the flow through it will be reduced.  Reduced aeration and oxygenation are the number one cause of tank crashes.  If there is not enough then it is no different from being trapped in a small room without ventilation, it is a death trap for the fish.  A tank crash and total fish death can happen within 24 hours without adequate aeration and oxygenation in the tank.  To prevent this from occurring you need at least one and preferably two or three alternate forms of water circulation and aeration.  A powerhead specifically designed for water movement is essential as and an air pump with some sort of bubbler is recommended as well.  In a saltwater tank a skimmer and an extra powerhead or two will suffice.  A battery powered air pump is definitely a good idea to have in the event of power failure that could last more than just a few hours.

Some form of biological filtration is also a big part of most aquarium filtration systems.  It is not always necessary but is very common and will help maintain the water quality and prevent tank crashes.  The most common form of biofiltration is fast flow aerobic bacteria biofiltration.  It can consist of biowheels, bioballs, or even just a sponge that hosts aerobic bacteria.  Oxygenated water flows over or through the media that develops bacteria which will reduce organics and ammonia and turn them into nitrates.  Nitrates will accumulate in the aquarium until they are removed by water changes or denitrification.  These bacteria will also be present in the water column, in the gravel, on rocks, and on the glass of the tank.  In lightly to moderately stocked aquariums there will normally be sufficient bacteria to perform this function but some type of other biofiltration is still a good idea to provide back up.  In well stocked aquariums it becomes necessary to control the organics and prevent ammonia spikes that can be caused by an unexpected fish death in the system.

There are hang on back filters and canister filters that can incorporate several forms of filtration at once such as physical filtration, biofiltration, chemical filtration, and sometimes even a UV sterilizer.  A sump is common in larger tanks where individual filtration and other components can used without having to be in the main tank.  Skimmers and denitrators will be separate components from any hang on back or canister filter.

Denitrification is another form of biological filtration.  With denitrification water typically flows through a relatively large and/or specialized bacterial bed at a relatively slow rate.  Aerobic bacteria can be present which reduces the oxygen in the filter and then anaerobic bacteria reduces the nitrates to gasses which then escape into the atmosphere with normal tank circulation and aeration.  Sulfur denitrators use sulfur to host specialized anaerobic bacteria.  Without denitrification water changes will be the primary way to reduce nitrates.  There are several other ways, such as a refugium, that can assist in reducing nitrates but they are limited in their effectiveness and capacity.  A slow flow comprehensive denitrator such as the Aquaripure Nitrate Removal Filter will replace some of the other biofiltration, especially in lightly or moderately stocked tanks but some fast flow biological filtration should still be used in well stocked aquariums.  Denitrification can definitely greatly reduce water changes and the amount of time and money spent on aquarium maintenance.