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Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary FILTRATION SYSTEMS The natural marine environment, especially the tropical marine environment, is an incredibly stable one with water chemistry fluctuating by only negligible amounts. Stability within the natural environment is however conferred by virtue of the enormous scale and capacity of the natural ecosystem. Stability within a smaller system requires much more sensitive management and careful balancing of both stocking densities and feeding regimes against filtration capacity. Getting the right filtration balance is essential in order to maintain stable conditions and remove the toxic waste products produced by the tank inhabitants. Aquarium filtration can be classified as mechanical filtration, biological filtration, chemical filtration and sterilisation. Filtration systems utilise one of more of these filter types when maintaining aquarium systems. Types of Filtration 1. Biological Filtration The biological filter utilised in the display is contained within the substrate. This filter bed provides the perfect environment for de-nitrifying bacteria to thrive and is host to the most important process involved in keeping aquatic creatures alive in the system. This is the site of breakdown of all bio-degradable waste via the natural denitrifying process known as the nitrogen cycle. In brief the substrate material has been chosen to present a very high surface area to volume ratio. The ammonia rich, oxygenated waters present an ideal environment for autotrophic bacteria to thrive. The various types of bacteria present break down ammonia, which is highly toxic to marine life, to nitrite, which is far less toxic, and to nitrate, which is virtually harmless. The substrate present in tanks is only one way of providing home for the invisible but essential tank inhabitants. Biological media or filter media and bio balls are added to the system to provide even more areas for these bacteria to reside. Bio towers incorporated in designs of some tanks as well as external canister filters can be filled up with these biological media. They are placed in the areas with the highest possible water turnover to ensure constant inflow of nutrients (fish waste) to the bacteria and also to keep them adequately oxygenated. For this reason, filter or pump should never be off for too long, otherwise all the bacteria die. 1.2 Biological Media The range of biological media products currently available is immense and one only has to try which type works the best for the set-up. They all have different texture, come in different shapes, colours, sizes and often have unique properties, eg. denitrifying, phosphate removing, odour reducing, etc. These are placed into a mesh 1 Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary bag and put into an external filter or bio tower along with other types of filter media (eg. filter floss, which is a type of mechanical filtration) and very often in conjunction with bio balls. Picture 1.: Examples of biological filter media. High surface area is owed to porous structure. 1.2 Bio Balls Bio Balls are plastic balls specially designed so as to provide high surface area versus volume ratio which gives the bacteria an immense space to colonise. Bio balls also come in many sizes, colours, shapes and designs. The main advantage of bio balls over other biological media is that the surfaces are impossible to clog up (when used with a prefilter) compared to the micropores of porus ceremic filter material. The reason is simple: the gabs of space within a bioball is large and anything that can clog it up would already have been filtered by the prefilter (such as filter wool, sponge, etc). This is the reason why water filteration should always pass through mechanical filteration (prefilter) before biological filteration. Bio balls also win over biological media as their high surface area isn´t based on miniature pores. While these can get clogged up even when a prefilter is in place, bio balls design prevents this from happening. Picture 2.: Bio balls come in a wide variety of shapes and designs. 1.3 Cleaning Cleaning of biological part of the filtration system is crucial and the correct procedure of doing so should not be underestimated. Bacteria take a while to get established and removing all parts of the filtration at once or rinsing it with freshwater will kill all the bacteria. Removing all bacteria leads to catastrophic spikes in ammonia and pH 2 Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary and ultimately to mortalities of tank inhabitants. If the filter isn´t designed for partial media changes, rinse the content in tank water. This way you will get rid of the material that´s has accumulated on the filter floss, in the pores of biological filter media or on the surface of bio balls but you will not kill the bacteria. If you are introducing any type of treatment to the tank, remove the filter from the system, otherwise the bacteria will be killed. In order to keep the filter running for the duration of the treatment, fill up a bucket with the pre-treatment tank water and let the filter running on this small circuit. Biological filtration on its own cannot support many fish though, and therefore need to be used in conjunction with other filtration methods. 2. Mechanical Filtration Mechanical filtration removes particulate waste and other suspended solids from the tank by trapping them in a fine medium. This medium can be sand, sponge, floss or wool depending on the size of the display. There are various types of mechanical filters and many of them also offer habitat for de-nitrifying bacteria and thus contribute to biological filtration to certain degree. That’s why when it comes to cleaning, whichever media is used, it needs to be washed in the tank water rather than fresh water. Regular cleaning to remove the built-up dirt is essential in order to prevent clogging-up or in the case of sand filters, the sand becoming too compact to be able to perform its function. 2.1 Pressurised Sand Filters Among the most complex mechanical filtrations systems are the pressurised sand filters. These are designed to remove the tank detritus, which is larger than 30-40 micron, much like a sieve works. The filter itself comprises of a container filled with sand that will filter out the debris as the water flows through it. Sand filters are often installed with a multi-port valve that makes operating and maintaining the filter easier. The position of the valve will determine which way the water enters and leaves the system. The condition of the filter can be also determined directly by the pressure gauge reading but the range of normality is sand filter specific. Picture 3.: Sand filter diagram and a multi-port valve. 3 Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary The sand bed and associated nozzles/collector laterals/candles on the base of the filter do not require any direct maintenance provided the plant is operated correctly. Particular attention should be paid to correct flow rates and backwashing. If the bed should become clogged due to improper handling this can usually be attributed to poor backwashing or excessive flow rates. Flows above those recommended will drive the dirt deeper into the bed, making it much harder to remove, thus requiring longer backwash. 2.1.1 Backwash Backwashing is the process of reversing the flow through the sand filter to remove any dirt trapped in the sand that may be reducing the filter´s efficiency. Without regular backwashes and maintenance checks, sand filters can become clogged or concreted, and prone to channelling. If the sand in the sand filter becomes clogged up and dense, not enough water will be able to flow through it and this consequently may affect other equipment plumbed onto the system, eg. inline heaters which need sufficient flow through them otherwise they will switch themselves off. In a scenario like this, quality of the entire system may become compromised and the filter is not functioning properly and a heater in not heating up the tank water. On smaller filters with a multiport control, the pumps must be stopped before the valves are adjusted The valve arrangement on the sand filter should first be moved to the backwash position then the filter should then be run for 5 to 7 minutes or until the filter has been completely flushed free. Picture 4.: Diagram of sand filter indicating the direction of water when filtering and when backwashing. 2.1.2 Rinse After backwashing is completed, the multi-port valve should be moved into the ´rinse´ position. This means the water will flow through the filter as though it was filtering but this time the water will be sent to waste instead of being returned to the tank. This ensures that any residual material that wasn’t removed during backwashing is removed now from the system. Rinsing should take 30seconds to 1 minute maximum. The pressure gauge should then be rechecked to ensure that the filters have been cleaned and the procedure repeated if necessary. 4 Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary 2.2 Under Gravel Filters Under gravel filters are an early form of filtration, however still popular as it is relatively cheap, easily available, yet very efficient. The base of the tank is covered with a plastic plate that has fine slits cut into it and this tray is covered by gravel. A tube leads from this tray, up the back corner of the tank, with an airline inside the tube. As the air rises in the tube it creates suction which draws the water through the gravel bed. Gravel bed in this case acts as filter media and thus harbours purifying bacteria. In order for this type of filtration to work properly, the gravel needs to be siphoned regularly to prevent clogging up of the slits on the gravel plate and also the prevent gravel residing bacteria from starvation of dissolved oxygen. It is important to limit the amount of decoration you put over the gravel plate, as this limits the flow and inhibits the filtration. It is also essential to ensure that the filter plate is completely covered at all times, as any gaps in the substrate or exposed plate will reduce the efficiency. The biggest drawback with an under-gravel filter is the potential for algae growth in your aquarium is increased. With all of the organic matter being trapped in the gravel with water passing through, the nutrients are redistributed into the water column feeding the algae. Picture 5.: Schematic diagram showing the direction of water flow through the filter plate. 3. Chemical Filtration 3.1 Carbon Chemical filtration refers to any filtering substance that is designed to change the chemical composition of the water, but most often refers to the use of activated carbon or other cleaning resins. Activated carbon pulls dissolved organics from the water by adsorbing them. Carbon is very effective in removing a variety of impurities, such as copper, chlorine from tap water, dissolved proteins and carbohydrates, 5 Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary heavy metals and ions, medications, etc. Removing all these substances from the system will make the water look crystal clear Activated carbon is made from various base materials that have been heated then steam-treated. The steaming process makes the carbon extremely porous. Porous substances have extensive surface area. As the water passes over carbon, the carbon chemically attracts pollutants that adhere to the surface of the carbon, including odours and colour. Since carbon works by chemically attracting pollutants to its surface, once the surface area is covered with dissolved organics, the carbon is exhausted and must be replaced. Depending on many factors, this can happen anywhere from a few days to 3-4 weeks. One signal that your carbon is exhausted will be a gold tint to the water. Picture 6.: Carbon pellets and process of molecular binding to carbon. 3.2 Zeolite Chemicals such as zeolite can be used in emergencies to remove ammonia from displays, but should not be used long term as it can destroy the natural bacteria needed to cycle the tanks. 3.3 Protein skimmer A protein skimmer or foam fractionator is a device used mostly in saltwater aquaria to remove organic compounds from the water before they break down into nitrogenous waste. Protein skimming is the only form of aquarium filtration that physically removes organic compounds before they begin to decompose, lightening the load on the biological filter and improving the water's redox potential. Although the process of foam fractionation is commonly known for removal of waste from aquaria, it is, in fact, a rapidly developing chemical process used in the large-scale removal of contaminants from wastewater streams and the enrichment of solutions of biomolecules. Protein skimmer removes certain organic compounds, including proteins and amino acids, by using the polarity of the protein itself. The water flows into a chamber containing millions of tiny air bubbles. These bubbles get coated in the protein rich water as they rise up through the chamber, and as the collect at the top they are pushed into a collection cup. The collection cup can be emptied and cleaned periodically, removing waste from the system. 6 Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary Effectiveness of the system can be maximised in several ways. The smaller the air bubbles in the chamber, the greater the surface area versus volume ratio and thus more compounds can be bound onto the air bubbles and subsequently removed. The length of time the air bubbles are present in the chamber of the skimmer also increases effectiveness. Foam collected in the collection cup should be as dry as possible as to decrease the amount of water removed from the system when emptying the cup. Picture 7.: Schematic diagram illustrating the function of a protein skimmer. 3.4 Ion exchange resin These filter media are less utilized than carbon, but are becoming more common. These work by attracting a specific molecule to adhere to them. Some attract ammonia or nitrate, and some remove dissolved organics. Ion exchange resins are also utilized in some carbon mixtures available on the market. The resins often strengthen the filtering ability of the carbon, as well as help biological activity by removing pollutants before they enter the nitrogen cycle. There are different methods to "chemically" treat the water. There are many different media that you can use in the chemical filter, and in different applications. Some of these chemicals include: carbon, zeolite, peat moss, calcium hydroxide, poly adsorption pads, and other chemically treated media. There are also many other additives, and vitamins to aid in supplementing the efficacy of the chemical filtration. 4. Sterilisation Ultraviolet light can be used in addition to biological, mechanical and chemical filtration. The UV light denaturates the DNA of free bacteria and pathogens as they pass through the filter. It also significantly reduces the risk of disease spreading in the tank and eliminates the risk of toxic tank syndrome caused by sudden bacterial or algal blooms. This was the UV filtration provides a measure of insurance against mismanagement of the aquarium system, however all efforts must be made to employ other types of filtration. Water passing through the UV filter must be clear in order for UV light to penetrate and for sterilisation to be effective. 7 Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary Picture 8.: UV light denaturates DNA at wavelength approx. 250-270nm. The peak wavelength of 264 nm is the most lethal to a living organism’s DNA, and prevents it from reproducing. Picture 9.: UV Steriliser mechanism 5. Filter Maturation Populating a filtration system with a colony of denitrifying bacteria is called cycling and this process is essential for a correctly functioning tank. Brand new system can be colonised by these microorganisms in several ways, which can also be used all at the same time. 5.1 Cycling If possible, gravel or substrate for another already populated, established and healthy tank can be used to speed up the process. This will seed the biological filter bed with the helpful bacteria and will accelerate the maturation of the biological filtration process. Establishment of de-nitrifying bacteria will take place naturally, without seeding, however the maturation process will take longer. The next stage is to introduce a source of organic waste. These pollutants are an essential food source for the bacteria and this starts the process of the nitrogen cycle when harmful ammonia is broken down to decreasingly harmful chemicals. 8 Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary There are several methods of how to start the cycling process. Fishless cycling involves using household ammonia or a designated aquarium waste substitute that mimics pollution. Adding biological starter fluid, powder or a capsule is known as seeding. In the case a gravel from a mature tank has been used, this step can be bypassed, however it can be carried out regardless. Cycling that relies on hardiness of some fish species to withstand poor water quality for the period of time the denitrifying bacteria need to establish themselves in the system, is called fish-in cycling. This means that the first pre-mature tank inhabitants are exposed to varying and often high levels of ammonia and nitrites and actions like this can rarely be justified. These fish, just like any fish, produce nitrogenous waste on which bacteria can feed and in return they will establish themselves in the system. Adding bacterial food source without adding bacteria is known as ´feeding´ the filter. Process of tank maturation follows certain pattern. In a closed system there will be a steady rise of ammonia whose levels will drop in conjunction with a rise in nitrite. When the level of nitrite collapses the filter is mature. Picture 10.: Ammonia, nitrite and nitrate levels changes during tank cycling period. To complete this process may take 2 to 3 months (3 to 6 weeks with quick maturing agent), throughout which time there is a very high risk to less hardy creatures. In a closed system only hardy creatures can be kept throughout this period and stocking densities must be kept low due to the toxicity of high nitrite levels. In an open system with regular water changes maturation process can be speeded up, however this also depends on the temperature of the tank. Cold water systems need more time to establish a fully functioning bacterial colony, while warm water systems are more efficient in this. Frequent water tests have to be carried out during an aquarium cycling to monitor the maturation process. 9 Filtration Systems Barbora Pucikova, Aquarist at the Scottish SEALIFE Sanctuary 5.2 After cycling After the tank has matured, regular water tests still have to be carried out in order to ensure the ammonia and nitrite levels stay at an acceptable level. See the table below for guidance on normal, acceptable and critical levels of these harmful chemicals. Ammonia Nitrite Nitrate Normal Level 0.1ppm 0.0ppm 0.0ppm Acceptable Level 0.2ppm 2.0ppm 2.0ppm Critical Level 0.4ppm 4.0ppm 20.0ppm If critical levels are reached on any of the above then a substantial water change must be done immediately to reduce the level to an acceptable one. Obviously it is preferable to maintain the above components between normal and acceptable levels by initial small frequent water changes rather than let them rise to critical levels which may necessitate water changes of up to 50%. 5.3 Ammonia and pH problems The massive increase in bacterial activity has the effect of depressing pH levels and this is a common problem in newly set tanks. Although hardy creatures will tolerate low pH for some time, the more delicate creatures may require a minimum pH value of 8.1. This will be maintained throughout the filter maturation process by regular water changes. pH stability will however ultimately be stabilised by virtue of the inherent buffering capacity of natural décor such as the calcium based substrate in most saltwater displays. 10