Aquarium Filtration

An effective filtration system needs to remove waste solids, oxidise ammonia and nitrite, remove carbon dioxide, and aerate the water before returning it to the aquarium. Waste solids are generally removed via some form of mechanical filtration, ammonia and nitrite via biological filtration, and carbon dioxide by the provision of an air/water interface. Aeration of the water is also achieved across the same air/water interface. In the average aquarium, all these processes are done within the tank. In more specialised aquarium systems, most if not all of the processes are undertaken external to the aquarium.

Proper biofilter design is critical for the success of aquarium filtration systems. A number of biofilter types have been developed and tested in aquacultural systems, but very little research has been conducted with aquarium filters. The ability of a filter to remove harmful nitrogenous compounds is affected by media type, flow rate/retention time, dietary protein source/ content, water quality, and filter design. Media type and quantity determine the amount of surface area available for bacterial growth.

Dietary protein source and content directly affect the amount of nitrogen that will enter the water. Interactions between these factors and with the biology and chemistry of the system must be considered. Filter media should provide maximum surface area with media particles and pore spaces large enough to minimise clogging. Retention time, which affects filter efficiency but not necessarily nitrification rates, is one of the most significant factors that must be considered in filter design and operation. Ammonia removal efficiency is most affected by retention time in the filter, hydraulic and ammonia loading, and amount of organics in the water.

Flow rate significantly affects the rate of ammonia removal. More ammonia was removed in filters with the flow rates of 57.5 L/hour than for 111 L/hour. The slower flow rate provided a longer residence time and allowed time for bacterial reactions to take place. Filter flow rate does not significantly affect nitrite levels, nitrate levels, fish growth rate or fish mortality. Dietary protein content will significantly affect nitrate level because of the varying nitrogen contents of the food rations, but will not significantly affect nitrite level or fish mortality (Brunty et al., 2005).

Maintaining healthy fish in an aquarium involves establishing adequate dissolved oxygen levels, removal of wastes, and sufficient ammonia nitrification. Aquarium fish produce a variety of wastes including faecal solids, ammonia, carbon dioxide and other materials e.g., uneaten food and dissolved substances that will accumulate in an aquarium. These wastes must be removed from the aquarium water or they become toxic to the fish. These accumulated wastes act as a nutrient source for bacteria that generate nitrogenous wastes, increasing the demand for oxygen, increasing carbon dioxide levels, lowering the pH, and contributing towards the deterioration of water quality.

While poor water quality may not be lethal, little or no growth as well as increased incidence of disease can result from poor water quality. Some researchers believe that there is a direct relationship between high levels of wastes and dense populations of disease organisms in aquaria, thus increasing the susceptibility of the fish to disease. Maintaining good water quality is of primary importance. Therefore, effective filtration or bioconversion must be provided to eliminate the effects that these waste products have on the rainbowfishes health and survival.

A properly designed filtration system will remove or reduce such wastes, and enable you to maintain your rainbowfishes for extended periods without drastic procedures, such as extensive water changes. All systems should have a method of removing particulate waste, a method to re-oxygenate the water and a method to recirculate the water. Each component of the filtration system must work in conjunction with other components of the total system. In choosing any filter component, you should keep in mind that it must be capable of maintaining an excellent environment for the fish. However, don’t expect any filtration system to provide perfect water conditions. Over a period of time the water quality will deteriorate and therefore must be changed on a regular basis and is a necessary part of your aquarium management program. Aquarium filtration can generally be accomplished by a number of methods:

Mechanical removal of undissolved, particulate • matter. Chemical removal of dissolved organic matter. • Biological conversion of toxic wastes to less toxic • materials. Any combination of the above. •

Removal of particulate matter can be accomplished by mechanical filtration through porous material such as sponge, screen, sand or gravel. Particles that are larger than the pore sizes in the filter media can clog the filter, and lead to reduced filtering capacity and efficiency. Most of the particulate are made up of organic compounds that will gradually break down in the system from bacterial activity. Although this process adds additional oxygen demand to the system, it reduces the need for frequent cleaning if the solids do not become resuspended or interfere with normal water flow. Mechanical filters require regular cleaning since they are prone to clogging.

Filtration systems should be designed for simplicity of operation. Sufficient time must be allowed for conditioning of the biofilter prior to introducing fish. Ammonia and nitrite concentrations must be checked frequently. Dissolved oxygen should be sustained above 5.0 mg/L and periodically verified. Alkalinity, hardness, and pH need to be measured and adjusted, if necessary, at regular intervals. Filters should be inspected and cleaned as required. Medications used to treat fish diseases may be toxic to bacteria in the biofilter. An ability to isolate fish tanks for disease treatment should therefore be provided.