Aquarium Filtration

What is the purpose of an aquarium filter? By Tim Gautrey

To clean the water of debris and suspended particles, remove ammonia and nitrites and aerate the water.

How does it work? Most filters are divided into three sections: Biological, Mechanical and Chemical. Biological. An aquarium filter is a breeding ground for two main types of bacteria. This is not something to worry about, quite the opposite. The type of bacteria that filters culture is specifically to work on the chemicals that fish produce through waste. The first type of bacteria breaks down the potentially very poisonous ammonia that fish produce into less harmful nitrites, and then a second type of bacteria breaks down the nitrites into even less harmful nitrates. Mechanical. The filters will also remove large suspended particles of debris from the water. Chemical. Some filters allow the addition of Active Carbon in the form of balls, sheets, wadding or crystals. The purpose of this is to remove medications and heavy metal traces from the water. Aquarium filters come in several different forms, from Under-gravel filter trays, through Hang-on-back (HOB) filters and internal power-head filters to external "Sump" filters. All of them do very similar jobs and all work well. The main criterion for choosing which filter is best is the size of the tank and the load you are going to put it under. Let's take them one at a time and explain the benefits and drawbacks for each. I'll start with the cheapest and work upwards in cost: Simple Air powered Filters: Air-box and foam filters, which sucker onto the sides of the tank or just stand on the bottom and contain a filter media, foam or wadding to hold the bacteria and filter out the large debris. These filters are very cheap, often costing just a couple of pounds. The principle of filtration is very simple, using an air stream to force the water through the filter. The principle use for these is in fry breeding, where you need a filter that doesn't cause strong currents and that won't pull the small fry into the internal workings. They also make ideal backup filters for other types and can be setup in minutes. You can even make your own filter like this out of bits and pieces you have laying around! If you have an air pump, you can use this type of filter. Dis-advantages: Regular maintenance is a must. These filters can clog up with debris very quickly in heavy load situations. Not able to handle heavy filtration. These filters are not suitable for tanks where you have diggers, as they clog up very quickly and are limited on the amount of bacteria they can support. You need an air pump to run them. Under-gravel Filter: Out of all of the above, this is my personal favorite. Apart from anything else, it is the cheapest and simplest to maintain. Over the years, these have become less popular, mainly due to commercialism, not in-effectiveness. (Retailers make more money by selling more expensive options) The filter works as follows: It draws water down through the gravel across the entire bottom of the tank through small slots in the tray and forces the cleaned water back to the top through riser pipes in the corner of the tank using either an air stone or a power-head. The filtration is done by the gravel removing the larger particles and the bactreria that lives in the gravel and under the tray removing the harmful ammonia and nitrites. With the Active Carbon filter attachment fitted to the top of the risers, it will also remove heavy metals and medications from the water.

Advantages: It aerates the water by means of the air stone which draws the water up the riser or simply by the disturbance of the surface in the case of power-heads. It regulates the water temperature throughout the whole tank, simply by drawing the colder water from the bottom and pushing it out at the top. With the heater placed beside the riser pipe, this water is heated back up straight away, giving more even temperatures. It is flexible. By the addition of another riser pipe, the filter is capable of carrying a much larger bio-load, which is very helpful for over-stocked tanks. Most trays come with spare riser sockets to add more risers if required. It is a low-maintenance system. If you are pushed for time, this filter is very forgiving. It won't stop working over a short period of time and can be left for weeks without any concern. It is safe to use with very small fish. So long as the riser pipe is above water level this filter is very safe for smaller inhabitants. It is good in planted tanks. Plants can root through the gravel and into the slots in the tray to get a good hold. The cost is minimal. these filter trays are by far the cheapest alternative of all the filtration systems. Disadvantages: Cleaning: Can be difficult if not carried out regularly. (See the article on UGF cleaning for effective and quick ways to clean these filters.) Air Pump: You need an air pump powerful enough to run this filter effectively. It pays to buy a good air pump as if the pump stops, the filtration stops too. Substrate: You are restricted with the types of substrate you can use. Gravel is the only effective type of substrate for this filter. If you want to use sand, don't use this filter! Efficiency: The filter becomes less effective if not cleaned regularly. By regular, I mean at least every six months, which is a lot less than other filter types. Noise: The filter itself is silent, but sometimes the air pump the runs it can be noisy, so and the sound of bubbles bursting on the surface all the time can get annoying. Careful selection of the pump is very important. Internal Power-head filters: By far the most common system used today, these filters come in a range of sizes and shapes to suit most small to medium sizes tanks. They simply sucker onto the side or back of the tank and connect to mains power. The filter works through an impeller drawing the water through the filter media and forcing it back into the tank. Advantages: Availability: There is a filter for most common sizes of tank. Simple to install: They can be fitted into a tank in seconds. Cleaning: The filters simply slide onto a bracket inside the tank, so removal for cleaning is easy. The media is contained in a removable section of the unit and can be made up of several elements, each one to do specific tasks. They can contain wadding, foam or crystals or a combination of any of the above. If they use foam pads, then you simply rinse them out and replace them when necessary, if they contain wadding, this can be rinsed a few times, but mostly requires replacement each time. Crystals will last for around 4 weeks at a time, then need replacing.

Noise: Most of these filters run quietly. Disadvantages: Looks: The physical size of the filter unit can be a problem if you want to hide it away. As it hangs inside the tank, it also takes up room and in a small tank, this could be a real nuisance. You need to take care when trying to hide it behind plants etc, as there must be clear passage for the water, otherwise it just won’t work! Cleaning: These filters must be cleaned regularly. They will clog up very quickly in high demand areas and become ineffective very quickly. Cost: They can be expensive to buy initially, especially the larger ones. The cost of maintenance can be high. Depending on the type of media used in the filter, it can get expensive to keep replacing media all the time. Water Currents: The current they create can be a problem. Some fish don’t like strong currents, and these fish do not do well in tanks with this type of filter. On the other hand, some fish love it! They also create a strong current at the intake, which can trap or even kill small fish and fry. HOB or Canister Filters: Hang on Back or Canister filters are becoming more common these days. I have prouped these two together since they are essentially very similar in performance and operation. They use two pipes that hang or clip over the back of the tank and water is pumped through the filter which can be on the back or anywhere away from the tank. Usually installed in a cupboard under the tank, but also wall-mountable. This type of filter contains lots of different types of media, depending on the manufacturer. Usually fairly expandable too, so individual choices of media can be made according to need. The recommendation for this type of filter is that it should be large enough to circulate ten times the volume of water per hour, which means that a 100 gallon tank requires a filter capable of moving 1000 gallons per hour! Advantages: Power: These filters tend to be very powerful and move a great deal of water, capable of handling high demands on medium and larger tanks. Some are also adjustable so you control the power it uses. Effectiveness: For diggers and bottom dwellers they are very effective, since they clean large amounts of water very quickly. On most tanks where these filters are fitted, they give crystal-clear water all the time. Visability: They are easy to hide away, since it is only the two pipes that enter the tank, and these are easy to disguise. Current: These units create a really strong current from both ends. The intake needs a good pre-filter fitted to stop the inhabitants being drawn in and the outlet creates a very strong circulation in the tank which is perfect for some fish, but not so good for others. Disadvantages: Cleaning: Can be difficult to clean and some need to be primed before they work. There have also been reports of flooding during the cleaning process, as when installed below the tank water level they can act as a siphon if the valves are not closed properly. Not so prone to clogging as they use lots of media. Cost: These are very expensive units, and maintenance costs can be high too, depending on the type you buy. The recommendations tend to insist on a much larger unit than you would expect to need. Noise: They can be quite noisy, the HOB filters especially, but canister filters can be installed away from the tank, this means that they can be put in another room if necessary. Sumps:

Although these are not necessarily the most expensive to buy, I have put them last because they are by far the most adaptable, but need a lot of skill and patience to set up, and the cost is totally dependant on what you use. A sump is a separate tank, usually a small 20 - 30 gallon fish tank, split into compartments for various uses. A sump is completely adaptable to suit individual requirements, and there are no real guidelines for this. Examples can range from a simple multi-stage filter, through internal heaters, live plants, biological additives, the list is almost endless. Mainly fitted to the larger tanks, care needs to be taken in the planning, location, building and use intended. Most sumps are purely DIY and usually only attempted by experienced aquarists. Unless you have a real need for this type of filter, stay away from it!

How To Choose Aquarium filtration. The topic of filtration for both aquariums and ponds is a huge subject. There are many types of filtration systems available and even experts disagree about which are the best systems. The basics are, however, quite simple and applicable to every type of captive aquatic environment. What Is Filtration? Filtration is a process involving mechanical, biological and chemical means to remove organic pollutive elements and other toxins that are present in an aquarium (Or other enclosed aquatic environment containing living organisms). A build up of liquid and solid fish waste primarily causes this pollution. Why Is Filtration Recommended? A filter will process the waste produced by fish in the aquarium providing a healthier, more stable environment. In a filtered aquarium fish will be much less prone to disease, more active and more colourful. Types Of Filtration Explained. A filter is a container that is filled with material called media. This media does two or three things: a) traps small particles of waste matter (Mechanical filtration) b) provides a large surface area which is colonised by a bacterium which consumes waste (Bacteriological filtration) and c) absorbs or converts other toxins which cannot be trapped or converted by a) or b) above (Chemical filtration). Most filters are supplied complete when purchased with a) and b) and the option for c) may be purchased separately. Bacteriological filtration is arguably the most important part of any filter function as this process will remove a component of fish waste called Ammonia, which is extremely poisonous to fish. Some types of chemical filtration can also remove Ammonia. Common Types Of Filter. The most common types of filter are Internal Power Filters, External Power Filters, Air Pump driven or Powerhead driven Under-Gravel Filters and Air Pump driven Internal Box Filters. Some Aquarium systems, such as Juwel, Mirabello, Eclipse, Tropiquarium and Fluval Uno and Duo come complete with manufacturers filtration kits already fitted. About Internal Power Filters. The filter consists of two sections. The top section is a submersible centrifugal pump which provides the power. The pump is attached to a canister, the bottom section, which contains a bio-foam. The bio-foam traps waste and provides a home for beneficial bacteria that consume physical and liquid waste. The filter unit is attached to the aquarium glass with suckers, back, side or corner, dependant on filter type or your choice of position. A modern internal power filter will, therefore, treat aquarium water in the following ways. Mechanical filtration. Water is drawn through holes in the canister and passes through the sponge inside so trapping small particulate waste. The benefit over traditional under gravel filters is that this waste is removed from

the aquarium entirely when the foam is cleaned. You will be amazed at how much waste is removed by the foam. Biological filtration. The bio-foam has a large surface area which becomes colonized by aerobic bacteria on its external and internal surfaces. The bacteria consume Ammonia, the most toxic component of fish waste, converting it into Nitrite (No2). Other bacteria also present convert the Nitrite into Nitrate (No3) which is a less toxic organic compound(s) and is subsequently removed by regular water changes and can also be absorbed by other filter media (See chemical filtration below). This process is known as the “Nitrite Cycle”. Chemical filtration (Not available with all filters). Many filters have a plastic core that is situated within the center of the bio-foam or other separate section. If present, this core or other section can be filled with absorptive filter media so providing chemical filtration. Media suitable are Zeolites (Sometimes called Ammonia Remover) and Activated Carbon. These materials polish the water removing organic toxins that cannot otherwise be removed by the filter unit. Additionally the water flow provided by the pump circulates the aquarium water and if positioned close to the water surface (Approximately 1cm ( ½”) below water surface) increases the Oxygen content as the water surface is rippled so increasing the surface area available for Oxygen absorption and other gaseous exchange Choosing an Internal Power Filter. Choosing an Internal Power Filter for your aquarium is easy. All manufacturers produce filters for a variety of aquarium sizes. Usually a number will identify the correct filter, ie. Fluval 2(Hagen), IPF2 (Interpet) which are for 2 feet or 60cm aquaria. Some manufacturers quote the volume of water that the filter is able to process (Eheim & others). To work out the capacity or water volume of your aquarium in UK gallons multiply the Length x Height x Width and then multiply this figure by 6.23 (Six point two three). If you require the volume in Litres multiply the result by 4.5 (Four point five). This gives the maximum water volume of the aquarium but of course, in real terms, there will be less than this as water is displaced equally by gravel and decorations so round the total down by 15 to 20%. See “How to work out the capacity (Water volume) of your aquarium” information page, for water volume of popular aquarium sizes. Maintaining an internal power filter. Follow the easy steps to make sure you get the best possible performance from your filter and ensure maximum life of the unit. STEP 1. Bio-foam maintenance. Before carrying out any maintenance on the filter unit always disconnect from the mains electrical supply. On average, the filter Bio-foam will need cleaning every 2 to 4 weeks. If the foam clogs up quicker than this (Evident by a much reduced flow from the pump unit) you are probably overstocked (Either in quantity or physical size of fish), or are overfeeding. Following manufacturers instructions for the particular filter, remove the Bio-foam. Squeeze the foam clean in waste aquarium water NOT tap water. If the foam is cleaned in tap water the beneficial bacteria it contains are killed, dramatically reducing the efficiency of the filter. For this reason it is best to carry out the filter cleaning operation together with the regular water change which should be carried out, on an average aquarium, on a 2 to 4 week cycle. Recommended water change is 15 to 20% of aquarium volume. Some systems such as Discus and Marine may require larger changes and/or greater frequency. See “ How to maintain a Tropical/Coldwater/Marine aquarium”) STEP 2. Motor unit maintenance. Before carrying out any maintenance on the motor unit always disconnect from the mains electrical supply. The motor unit is the top part of the filter. It will usually separate easily from the canister beneath which contains the Bio-foam. Refer to manufacturers specific instructions if unsure. In the centre of the motor unit is the drive part that is made up of a cylindrical magnet attached to radiating plastic tines looking something like a little

propeller. This is known as the impellor. Remove the impellor and clean off any sludge or other attached debris. Clean out the cavity into which the impellor sits. Replace and re-assemble. It is important to do this on an average system about every three months minimum. Failure to clean the impellor will create excessive load on the motor unit and reduce the life of the filter. STEP 3. Improving performance. Regular maintenance as described above will ensure maximum efficiency but the performance of the filter unit can be further enhanced by addition of Bio agents. These are usually in liquid or powder form and contain beneficial bacteria which, when added, boost the ability of the filter to consume waste. The UK’s best selling additive is “Cycle” by Hagen but most companies produce an alternative, many of which are featured on this website. These agents are highly recommended. How to choose and maintain an external power filter. About External Power Filters. External Power or “Canister” filters are available from most major aquarium product manufactures and provide a potent and powerful means of controlling the artificial environment of the home aquarium. These units are the next step up from the Internal Power filter. Although more expensive than in tank units they do offer a number of benefits. The filter is a large cylindrical or square container containing the media and the top part contains the motor drive unit. The media container and the motor unit are fastened together by clips and a seal between these two parts prevents leakage. Situated remote from the aquarium they work by drawing water from it by means of a slim intake tube in the water with a strainer on the end to prevent drawing in fish or anything too large for the filter to handle. Aquarium water then passes to the filter via a flexible pipe where it is processed by the media contained within. Treated water is returned to the aquarium via another flexible pipe terminating in a spray bar. The spray bar is a long, thin rigid tube perforated with small holes and can be positioned above or below the water surface. All filters are supplied as a kit, which includes all connecting pipes. Some, but not all are supplied with basic media and taps allowing disconnection of the main unit from the intake and spray bar pipes for ease of removal during maintenance. If they do not come complete with media and taps these can be purchased separately. Most manufacturers offer a range of accessories to complement the filter kit. Benefits of an external power filter. Much physically larger than Internal Power filters they are able to hold a great deal more filter media and, therefore, process more waste so ensuring the provision of better water conditions. The motor units are more powerful and able to deliver a higher, more consistent flow rate. Several types of filter media can be contained within the canister so the aquarium water can benefit from multi process treatment, biological, mechanical and chemical filtration. Some internal filters can also offer multi treatment but they are limited by the volume of media that can be contained. Additionally, material can be included to specifically alter the water chemistry such as peat extracts for Discus aquaria. Because the filter contains more media, which will be able to trap, as well as process large amounts of waste, the periods between essential maintenance are reduced. As the whole unit is situated external to the aquarium, either underneath or to one side so there is less equipment visible inside the aquarium. Choosing an external power filter. Choosing the correct external filter for your aquarium is easy. These filters are only suitable for aquariums of capacity 17 gallons (75 Litres) or greater. As a general rule, choose a filter which can turn over the entire aquarium volume between 2 to 6 times every hour with 4 times an hour being a good average rule of thumb . Calculate for a lower turnover for aquariums containing low stock densities or small fish and choose one with a higher turnover for heavily stocked aquariums, those containing larger fish or fish which require particularly good water conditions such as Discus or Marines.

Maintaining External Power Filters. See details on maintaining an internal power filter above and also refer to manufacturers instructions and filter media information pages. On average an external power filter will need maintenance attention every 4 to 8 weeks dependant on aquarium type and fish stock density. External canister filters are well worth the extra outlay and are highly recommended by Lifeforceonline. Under Gravel filters – Air Driven. Under gravel filtration is a traditional form of filtration that has stood the test of time and works but has largely been replaced by powered filtration and manufacturers kits that include filtration with the aquarium package. About Under Gravel Filters. An under gravel filter comprises a perforated plate positioned on the bottom of the aquarium which is covered entirely by the aquarium gravel. Affixed to the plate are one or two “Uplift” tubes that rise from the perforated plate into the body of aquarium water above. An “Air stone” is positioned just above gravel height inside the uplift tube and a length of hollow airline connects this air stone to an air pump situated external to the aquarium. The air bubble stream rising up through the uplift tube pushes water before it. This water is drawn from underneath the plate below and to replace this water displacement, water from the body of the aquarium is drawn through the gravel and down underneath the filter plate. In this fashion all the water contained in the aquarium is placed in constant motion from the body of the aquarium, through the gravel bed, underneath the filter plate and back up the uplift tube into the body of the aquarium. The aquarium water contains both oxygen and organic waste produced primarily by the fish inhabitants. The gravel layer above the filter plate becomes colonized by aerobic nitrifying bacteria which utilize the waste as a food supply, breaking it down into less toxic components and so purifying the water. This system works very much like the large gravel beds that can be seen at sewage processing sites. It is important that, should the air pump be positioned below the water level, a non- return valve be fitted. This will ensure that in the event of an interruption of the electrical power supply water will not siphon from the aquarium, down the airline and into the pump mechanism so avoiding a potential safety hazard. Instead of using an air pump the under gravel filter can be “Powered” by fitting a Power Head or Centrifugal pump to the uplift tube. This will make the under gravel filter more efficient as a power pump will produce a greater turnover of water through the filter bed than an air pump can. In addition the powered option produces a more consistent flow rate, which provides for a more stable filter bed and these pumps are almost silent in operation, unlike air pumps, which are noisy. Choosing An Under Gravel Filter. When choosing an under gravel filter it is important to choose one that is of a size that will, as far as possible, cover the entire base area of the aquarium. This is to ensure maximum circulation through the largest possible area of substrate. The slot sizes in the filter plates will vary dependant upon the make so check that the gravel type you are using is not of too small a grain size or it will drop through the filter plate slots. If this happens the void under the filter plate will clog which will reduce the filters efficiency or cause its function to cease entirely with disastrous consequences to the inhabitants of the aquarium. Maintaining Under Gravel Filters. In theory the filter bed should break down all waste produced in the aquarium but in practice the amount of bacteriological activity in most is insufficient to do this and there is, therefore, a gradual build up of silt within the filter bed. The performance of the filter bed can be enhanced with bacteriological additives such as “Cycle” but even with such assistance, regular maintenance is required to avoid overload and system collapse. A typical system collapse will occur quickly with catastrophic results as toxic Ammonia is released resulting in a “Wipe out” with loss of most or all of the fish stock. To avoid such an occurrence it is essential to maintain the gravel bed every two to six weeks with a four-week period being average. To do this use a gravel cleaning siphon device. This is a large bore siphon tube connected to a flexible discharge pipe. The large bore tube is pushed into the gravel bed once the siphon is started and mulm is drawn from the gravel with the water flow into a bucket recepticle.

Internal Air Driven Box Filters. These filters, as the name suggests are small plastic boxes that fit inside the aquarium to the back or rear corner. They can be filled with filter media such as filter floss and activated carbon and utilize an air pump to produce a water flow through this media very much in the same way as under gravel filters. This type of filter is now only used in very small or budget systems, temporary set ups and also sometimes in breeding tanks. They can also be used as temporary additions to existing filtered systems, for example when packed with activated carbon to

remove traces of chemicals after treatment to the aquarium.

Activated Carbon For many years, carbon has been used as an agent to remove impurities from air and water. Activated carbon is one of the most effective absorbents currently used. Activated carbon is carbon which has a positive charge added to it, which makes it much more effective at absorbing impurities and chemicals. An activated carbon filter works by the law of attraction. When water passes over the positively charged carbon, the impurities in the water which have a negative charge will be locked into the activated carbon filter. Usually activated carbon filters use either granular activated carbon or powdered block carbon. Both types of filters are effective, however the powdered block carbon filters do tend to remove more impurities than its counterpart. The efficiency of activated carbon filters are dependant on two factors. First, the amount of activated carbon which is contained in the filter and second, the amount of time the impurities stay in contact with the carbon. Of course the more carbon there is in the filter, the better it will do its job. Contact time of the impurities and the carbon can be affected by the flow rate of the water, thus slower running water is best. The more carbon you have, the better your results will be. If you set your water to a lower flow rate, the carbon will have more time in contact with the water contaminants, enabling the carbon to absorb the contaminants much better. When you purchase your activated carbon filter, keep in mind that they are rated based upon the average size of the particles they are able to remove, the most effective one being rated at 0.5 microns. The least effective activated carbon filter you can buy is rated at 50 microns. Most counter top activated carbon filter systems contain between twelve and twenty-four ounces of actual carbon. There are three main carbon types that can be used for the purpose of water filtration: coconut shell, wood, and bituminous carbons. The most expensive of the three is the coconut shell carbon; however, it has been proven to be the best out of the three types. Activated carbon is able to remove contaminants from your fish tank via two different methods, either through absorbing the contaminants, or through catalytic reduction, in which the negative ions contained in the contaminant are drawn to the positive ions that make up the carbon. Generally, organic particles can be removed via absorption, while chemical contaminants, such as chlorine, are removed by catalytic reduction. Many home water purifying systems use activated carbon filtration. Activated carbon filtration helps to remove the chemical bad taste from your tap water, absorbs unpleasant odors, and takes out many of the chemicals used in the water treatment process, such as chlorine. It also helps to remove many organic water contaminants as well. Activated carbon filters can also help remove many of the heavy metal compounds that are found in your tap water. Some more expensive activated carbon filters have been proven effective at removing some of the iron, hydrogen sulfide, and manganese that live in tap water. There are some inorganic particles that cannot be absorbed by activated carbon filters, such as arsenic, asbestos, cadmium, chromium, copper, fluoride, thallium, and mercury. To remove these kinds of contaminants you have to have either a reverse osmosis filter system or a water distiller.

Adding a sediment filter can help make your activated carbon cartridge last much longer as it removes larger particles that can possibly cause a clog, limiting the effectiveness of your activated carbon. To remove large quantities of sediment, you should consider using a carbon block filter rather than an activated carbon filter. The good thing is that you don’t have to do very much maintenance for your activated carbon filter, other than make certain it gets replaced as needed. To prevent your water quality from being effected, make sure that you change the filter promptly as recommended by the manufacturer.

What is Activated Carbon? By Andrea Watts - In its original form, charcoal is very light due mainly to its porosity. It contains phosphorous, sulphur and heavy metals - all of which are highly undesirable in an aquarium. It is sourced from the combustion of wood, lignite, bituminous coal, peat, or coconut shells. The activation process involves either thermal (carbonization and gasification) or chemical (with zinc chloride or phosphoric acid) reactions. These processes eliminate all impurities (elements other than carbon), and increases the overall porosity. Activated carbon is marketed for aquarium use and is available in powder and granules. It can either be purchased in convenient sachets (which are simply placed into the filter), or as loose matter used to fill a specialized compartment. It is very important that the carbon is thoroughly rinsed to remove the dust or residue that is produced during its manufacture.

Why use Activated Carbon? Chemical absorption is a basic principle of aquarium filtration i.e. the removal of impurities. This occurs when the undesirable molecules are trapped in the pores and outer surface of the carbon. The filter’s performance is linked to the available surface area, and therefore to the porous nature of the material contained in the filter. There are conflicting theories arising from the use of activated charcoal in an aquarium. Firstly, some people believe that it should be used permanently. The second school of thought promotes the occasional use of carbon. Personally, I believe that generally it is unnecessary to use filtration over activated carbon continuously. It is best used in response to particular requirements, such as the elimination of toxins, medicinal residue, or pigments such as tannin (given off by wood or peat). Filtration over activated carbon can prove useful in the long term to treat water containing high concentrations of undesirable substances like chlorine, chloramines, alum, phenols and insecticides and pesticides. Reverse osmosis systems are usefully coupled with activated carbon pre-filters. Used in conjunction, they eliminate chlorinated by-products than can damage the membrane. However, they are not very effective in the removal of nitrogenous by-products. Only the rigorous upkeep of biological filters and efficient biological filtration can help eliminate ammonia, nitrite and nitrate. The Negative Impact of Activated Carbon Activated carbon can be criticized for its inability to differentiate between “good” and “bad” molecules. It also fails to retain important trace minerals, including those needed by many hard water fish species and many plants. In reality, the adsorption power of activated carbon is dependent upon the different parameters (e.g. pH of the water) or the chemical form under which the element in question is found. The power of adsorption is limited and it losses its fixation capacity after several days, once it has become saturated. Even worse, it may then release the molecules it had previously extracted back into the water. Therefore, it must be replaced frequently; frequency being dependent on the saturation or concentration level of undesirable elements in the aquarium.