Guide to Water Quality

The Low Down On Aquarium Filtration Why And How

Why Filtration for Aquariums?

Aquariums are really artificial homes for our fish, these confined spaces without freely running water and proportionality a extremely high numbers of fish per litre of water require the support of technology to maintain conditions in which fish can survive and flourish. All fish produce a range of waste products that, if they are allowed to accumulate within the aquarium, will lead to a decline in water quality and fish health. Whilst stringent feeding practices and regular water changes may help, most aquarists will rely upon some form of filter to remove and break down these potentially toxic waste products.

The Filtration Process

Aquarium filters may be considered as a mechanism by which waste laden water is circulated through a chamber that contains a large surface area on which solid wastes may become trapped together with a surface on which an entire population of waste consuming micro-organisms are encouraged to grow. The portion of the filter that is associated with trapping solid debris is often referred to as the mechanical filter whilst the surface on which the waste consuming micro-organisms are encouraged to grow is referred to as the biological filter.

The mechanical portion of the filter often consists of a disc of foam or filter floss that allows clean water to pass through but traps any solid debris that enters it. Eventually, as the foam or floss becomes clogged with solid debris, the amount of water that can pass through the filter becomes restricted and both water quality and water clarity may begin to deteriorate. The process of trapping solid waste materials is referred to as mechanical filtration.

Although many species of fish produce a great deal of solid waste matter, an effective aquarium filter will also be required to encourage the growth of an entire population of waste consuming micro-organisms. These micro-organisms grow on the surface of the biological filter media where they feed on those toxic soluble waste products that are produced by fish. Although over 400 species of micro-organism have been identified as feeding on these soluble waste products, most can be divided into two main groups; those that consume ammonia and those that consume nitrite.

Even the smallest accumulation in soluble waste products is likely to have a detrimental impact on the health of fish and, therefore, should be avoided. The symptoms of a build up of this form of waste includes a depressed feeding response, excess mucous production and gill damage. Long term impacts of waste accumulation are much more subtle and include poor growth rates, reduced breeding response and suppression of the immune response.

The most important, and toxic, soluble waste product is ammonia. Although ammonia is excreted by the fish as a response to using high protein feeds, it is also produced when solid waste products are left to decay within the aquarium or mechanical filter. The other form of waste product that is associated with fish keeping is nitrite, which is excreted as waste product by those organisms that feed on ammonia. These nitrite consuming organisms also excrete the waste product nitrate. Although nitrate can be toxic to aquatic organisms, it is required to build up to significantly higher concentrations than both ammonia and nitrite before it will have an impact on fish health. Using high quality feeds and regularly siphoning or removing any solid debris remain as some of the most important but overlooked methods of maintaining water quality and enhancing the performance of the filtration system.

The process of biological filtration not only requires a steady supply of ammonia to encourage the growth of a stable population of waste consuming organisms, but it also requires a supply of dissolved oxygen, a stable water temperature and water chemistry. Any disruption to the quality or quantity of water entering the filter may disrupt or destroy this population and lead to a potentially lethal decline in water quality. Maintaining a stable water quality , ensuring that the water entering the filter is well aerated and preventing any blockage or disruption to the flow of water through the filter remain as the most effective methods of ensuring that the biological filter functions effectively and maintaining fish health.

Importance of Checking Water Chemistry

The process of encouraging a colony or population of waste consuming organisms within the biological filter can represent one of the most important tasks within fishkeeping. Water quality will quickly deteriorate if fish are added to the aquarium before this population has grown and established at a level at which they are able to consume all of the associated waste products. This period of time is often referred to as the maturation period.

At the early stages of the maturation period, the population of waste consuming organisms will be virtually zero and waste products are likely to accumulate quickly. The fishkeeper should be prepared to add only small numbers of hardy fish that are able to tolerate any deterioration in water chemistry, feed very sparingly and test the water for ammonia, nitrite and nitrate during this initial stage. Detecting even the slightest presence will require the fishkeeper to undertake water changes, add suitable chemical media, reduce feeding or remove any accumulating solid debris to enable them to return these toxic waste products to a safe level before they consider adding any further fish to their aquarium.  

Choosing a filter

Although there are many types of filter available to the fishkeeper, the most commonly used filters are the internal canister filters, external pressure filters, hang on filters and air driven undergravel filters. Each design of filter has a number of advantages and disadvantages that may influence the fishkeeper in making their choice.

Internal canister filterssited within the aquarium, the internal cannsister filter can combine both mechanical and biological filtration to provide an effective means of preventing waste accumulation within the smaller aquarium. Waste laden water enters through the base of the filter and is pulled up through the filter media before it enters a small impellor chamber from where it is pumped back into the aquarium. Although they are comparatively cheap and easy to install, the small size of most canister filters does usually restrict their use to lightly stocked aquariums. With the inlet located at the base of the filter, the aquarist may also find that much of the solid waste material that is generated within the aquarium may remain within the aquarium. Maintenance requires the entire filter to be removed from the aquarium which may require the aquarist to disrupt the aquascape / aquarium décor. Cleaning the comparatively small volume of filter media may also lead to a considerable level of disturbance to the function of the filter.

External canister filteroften located out of site below the aquarium, the external canister filter is probably the most effective form of filtration for the aquarist. Waste laden water usually siphons through a single inlet and a length of pipe before it enters the cannsister. The water rises through a series of mechanical, biological and chemical filter media before it enters an impellor chamber from where it is pumped up through a length of pipe before it is directed into the aquarium, usually through a spray bar. Many of the more advanced designs of canister filter that have been specifically designed for marine aquariums may also contain an in built ultra violet steriliser which will help to reduce the incidence of pathogens (disease causing organisms) within the inhabitants. Maintenance usually involves turning off the flow of water, opening the canister and removing the individual cages that contain the filter media. Consequently, any disturbance to the aquarium décor or the overall performance of the filter is minimised. Although they are comparatively more expensive than other forms of filtration, the external cannsister can circulate a larger volume of water and is capable of supporting a larger number of fish.

Hang on filtera relatively recent design, the hang on filter sits on the outside edge of the aquarium and provides the aquarist with an easily accessible and effective means of filtering their aquarium. Water is siphoned from the aquarium into the filter chamber and then into a powerhead from where it cascades over a lip and back into the aquarium. The unusual design enables the aquarist with a means of filtering those aquariums that have a complex aquascape / décor or a means of adding an additional means of filtering a mature aquarium.

Undergravel Filteralthough it may have been superseded, the undergravel filter provides the aquarist with a simple to install and easy to maintain filter that has a long history of success. The undergravel filter consists of an open mesh or filter plate that is supported off the base of the aquarium and an open tube or uplift tube that connects the plate with the upper surface of the water. An air stone pulls water through the uplift tube which then sucks waste laden water down through a bed of gravel that covers the filter plate. Solid waste is trapped within the upper layer of the gravel bed whilst soluble wastes are digested by the micro-organisms that colonise the surface of the individual particles of gravel. The aquarist will be required to clean the filter on a regular basis as the larger particles of debris will eventually begin to obstruct the flow of water through the gravel bed. 

Wet and Dry Trickle Filters – by encouraging a high concentration of dissolved oxygen within the filter, the wet and dry trickle filter is acknowledged to provide the conditions that encourage the optimal growth of the specialist micro-organisms that are responsible for biological filtration. Waste laden water is pumped up into the filter unit located within the hood of the aquarium and is then allowed to trickle down through the filter media. One portion of the filter, the ‘dry section’, is designed to encourage this waste laden water to trickle across the surface of the media, ensuring that the waste consuming micro-organisms come into a close degree of contact with any waste products. The close degree of contact between the water and the air that pervades the filter also helps to ensure that these waste consuming organisms are provided with the high concentration of dissolved oxygen that they require to function effectively. The dry section of the filter also boosts the concentration of oxygen that enters the submerged or ‘wet’ section of the filter and helps to ensure that any waste products are consumed by the rich, thriving population of micro-organisms that inhabit this section of the filter.   

Aqua One Top Tips

The Correct Size of Filter

Most filters are graded in accordance with the volume of water that they are able to circulate around the aquarium. As a broad rule of thumb, a tropical freshwater aquarium will require a filter that is capable of circulating the entire volume of the aquarium between two and four times per hour whilst a tropical marine aquarium will require a filter that is capable of circulating the volume of aquarium between four and six times per hour.

When to Add More Fish

Adding a small number of hardy fish and feeding them sparingly is one of the most effective methods of encouraging the growth of a population of waste consuming organisms on which the filtration system is based. However, as water quality may fluctuate whilst this population of waste consuming micro-organisms establishes, the aquarist must check that water quality is acceptable before adding any new fish to their aquarium.

Filter Maintenance

The population of waste consuming micro-organisms that inhabit the biological filter require a constant supply of oxygen and waste rich water. Depriving the filter of a flow of water for an extended period of time will deny these organisms of this supply of oxygen and waste, causing them to die and water quality to deteriorate. Consequently, the aquarist should always be prepared to minimise the period of time in which they maintain their filter and should always be prepared to monitor water quality for the period of time following any disturbance until water quality has stabilised. As a brad rule of thumb, depriving the filter of a supply of water for less than 20 minutes is not likely to have a long term impact on filter performance.


Feeding and Filter Maintenance

The amount of waste products that a filter has to cope with depends upon the amount of waste produced by the fish which, in turn, depends upon the amount of food that they consume. By feeding a constant amount of food on a regular basis, the aquarist can maximise the size and activity of this population of waste consuming micro-organisms, which in turn will ensure that water quality does not deteriorate.


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