My first article covered how to set up the basics of a new tank, and I briefly covered the filters. I’d like to go into a little bit more detail here on how to maintain water clarity, and to keep the fish happy. There is a lot of material out there on this, so without duplicating too much unnecessary information, I will try and keep it to the basics. First of all, you need to familiarize yourself with what is commonly known as the Nitrogen Cycle. If I recall back to my school days, this was taught in grade 10, (standard 8) biology, so those of you who didn’t venture into Biology as a preferred subject, then I will cover the basics of it for you. Some of us here are so far out of school, that we don’t even remember covering this in school. In order to assist me to put this in the most simple terms, as well as provide the necessary information, I am going to paraphrase a post that Professor Dirk Bellstedt provided, as I cannot put it any better. (Original text is found here: http://www.tropicalaquarium.co.za/showthread.php?t=2579 ) “The term “nitrogen cycle” is used in biology for the breakdown of ammonia to nitrite and nitrate in an aquatic system. In a balanced eco-system, the nitrate is then used as the building blocks of plant growth, and thereafter converted back to ammonia and nitrites and now you have a cycle. In our tanks, we are usually only dealing with one side of the cycle, as our plants are not absorbing the nitrates fast enough. For this reason we should not talk about cycling but rather "biological filtration" which is the correct technical term to be used. In a new tank, the fish start producing ammonia. (Ammonia is also produced by excess food breaking down, as well as decomposing plant matter in the tank). The bacteria that turn the ammonia to nitrite start off first (Nitrosomonas) , then the nitrite levels start going up and the second type of bacteria (Nitrobacter) start growing and convert the nitrite into nitrate. Ammonia and nitrite are toxic to fishes, nitrate less so, but you cannot have levels over 20 mg/l in your tanks as this then does becomes toxic to the fishes and you have to remove this by water changes.” So basically Nitrosomonas bacteria break the ammonia down to nitrite. The Nitrobacter then break the nitrite to Nitrate. When you start a new tank, you will find, through the aid of a good test kit, you will first go through an ammonia spike (because the Nitrosomonas have not populated the filter yet). After they have populated the filter, they will rapidly break the ammonia down to Nitrite, and you will go through a nitrite spike, until the Nitrobacter populate the filter. Both the ammonia spike, as well as the nitrite spike can be hugely detrimental to your fish. Nitrates, although they are used up by the plants, will start to climb in levels in your tank as well. The only way that I can effectively advise removing Nitrates is through regular weekly water changes of between 10-25% of the tanks volume. With a good testing kit, you will be able to determine over time how much water you should change, as each tank will have its own cycle based on the number of fish in the tank, as well as the number of plants. Now you understand why a good aquarist will “cycle” his tank first for 10-14 days before adding any fish to the tank. The problem with cycling is that because there is nothing creating huge amounts of ammonia, the Nitrosomonas do not populate the tank. This is where the chemical cultures of bacteria are advised to be added to the tank during the cycling process. The chemical cultures are basically all the beneficial bacterium that you want to populate in the filter in order to facilitate the nitrogen cycle. These are commercially available from most good Local Pet Stores (LPS), and should be added to the tank according to the bottle instructions. It has been suggested that you could add a pinch of fish food flakes to the water to speed up the colonizing of the bacteria on the filter, but this has neither been confirmed nor denied scientifically in the readings I have done. Some people believe in cycling a tank with a hardy fish that can take certain amounts of ammonia and nitrite spikes. I have heard that guppy’s and Danios are fairly hardy fish, but I personally feel this to be a cruel way of cycling your tank. That’s the nitrogen cycle; now let’s see what the big deal about having the right filter in your tank is all about. Well, in my previous article, I covered in a fair amount of detail on filtration, and how to go about choosing the correct filter for your set up. Let me cover a bit more in detail here on the 3 types of filtration available to you, and give you a little more help on choosing the right filter- Mechanical Filtration This is typically the first part of a filter that the water will pass through. This is usually filter floss and/or a sponge. The basic principle of the mechanical filtration is, as the name suggests, to mechanically (physically) remove particles in the water. This would include excess fish food, plant matter that has broken down, and fish waste. Bacteria can also colonize this medium. When I clean my filters (once a month) I completely replace the filter floss, as this usually gets a lot of gunk and muck on it, and I simply rinse out the sponge in water from the aquarium. NEVER EVER clean filter material in tap water. The chlorine in the tap water will kill of any beneficial bacteria that you have. Biological filtration This is typically the second phase of filtration. There are a wide variety of materials available for use here, but basically they all do the same thing. This is the core of the Nitrogen Cycle. This is where the beneficial bacteria populate by the millions. This filter media, (commonly Bio balls, ceramic rings, ceramic chips etc) is usually designed to offer a very high surface area for the bacteria to grow and live on. I have heard claims by some companies that 1 cubic cm of ceramic rings is equivalent to 1 square meter of surface area for the bacteria to colonize on. Whether this is true or not is irrelevant, the fact still remains that this is where the bacteria populates. I personally very seldom clean this medium… and will at most only rinse it very briefly in aquarium water. NEVER EVER completely replace the biological filtration part of your filters. If you have to replace it, replace only half of it at a time. Chemical filtration This is typically the last filtration media that the water will pass through before being pumped back into the tank. There are many types of chemical filtration medium available on the market, and each provides a certain type of filtration. This medium chemically takes certain stuff out of the water that you do not want. The most common chemical filtration is (1) Charcoal, (2) Purigen, and (3) Zeolite. Charcoal is used to provide your tank with that crystal clear appearance. A lot of aquarists do not keep charcoal in permanently. Charcoal also only lasts for about 4-6 weeks, and thereafter would need to be replaced. When medicating your fish, most of your medications would be removed by charcoal. So in order to effectively medicate, you would need to remove the charcoal, follow the course instructions on the medicine bottle, and then use charcoal to remove the meds thereafter. Purigen is also used by a lot of aquarist to clear up their tanks. It is a great chemical filtration medium to clear up the tank when wood leaches out tannins into the tank. Purigen get’s depleted, but fortunately it can be rejuvenated a few times before it becomes completely useless. Zeolite is used to remove Ammonia. It also get’s depleted, but again, this can be restored a few times too. In a tank, you would typically want a filter that does all 3 types of filtrating, and should you get a filter that is correctly rated for your volume tank, with the correct filter medium inside, you should have no problems in keeping your fish water in good conditions. (This is assuming you are not overstocking the tank, and do your water changes every week.) When you start to notice the water changing colour, you need to look at your chemical filtration, if you are running it, or look at including it if you do not have any. (Obviously algae are a completely different issue here). Fish are dependant on you as the aquarist to ensure that their water quality is good at all times. In the wild the fish are subjected to new water all the time through rain and streams. The moment your fish’s health starts depleting, the first thing you should do is check your nitrites, ammonia and nitrated level, if any of these are out of synch, you will need to take the necessary action. Ideally you want your Nitrites at 0ppm, Ammonia a 0ppm and Nitrates anything below 20ppm. (PPM = Parts Per Million, and is the measurement that my test kit measures these levels. Some test kits will measure in milligrams per litre) To put what I am trying to say in a nutshell: Your water quality, and hence the fish’s health, is dependant on you having EFFECTIVE filters in your tank, and a good maintenance plan in place. Cleaning a filter should only be done in water taken out your tank, as again I stress, water from the tap will kill off the bacteria. Let’s cover some of the most common filters: * (1) Hang-on-Back filters hang on the back panel of the tank. You would need to custom cut your canopy in order to fit this. A pump sucks water from inside the tank, and feeds it through the filter medium before it is poured back into the tank. The only draw-back to these filters is that you have to cut the canopy to fit it, and often the cheaper options can burn out. During a power failure, the water drains out of the filter. When the power is restored, unless you prime the filter, it will be running on air, and burn out. The more expensive filters prevent this from happening, and are often either self priming, or do not release the water when the power goes off. * (2) Internal canister filter basically sit inside the tank on the side. This has a “basket” whereby your entire filter medium is kept, with a pump on top that draws the water up. These are the most cost effective, and are often sold to new aquarists as they are the easiest to maintain. The biggest draw back on these is that they take up space inside the tank, and you will understand that the bigger the tank, the bigger the filter will need to be. * (3) External canister filter sit on the floor or in the cabinet of the tank. Water is siphoned into the filter via gravity into the canister, where it passes through different levels of filter medium, before finally being pumped back into the tank. These are in my opinion some of the best filters as they do not require much custom cutting to the canopy, they are outside the tank making maintenance a lot easier, and take up very little, if any, space in the tank. Some of the more expensive ones have a UV light inside them for extra filtration (not always recommended, but a nice to have feature when needed), as well as having the heater inside some of them. * (4) A sump where water is fed to a bottom tank usually hidden under the tank, passes through different chambers where you have your filter medium, and then pumped back into the tank. These are in my honest opinion, the best type of filters you get, and because it is a second tank sitting under the tank, it also increases the volume of your tank by that much. If you keep your fish in a 100litre display tank, running on a 50litre sump, you effectively have a 150litre tank. The sump is also the most difficult to get right, as, if done incorrectly, you can land up draining half your tank, and flooding your room when the power goes off (because the pump in the sump will not be pumping the water back up to the display tank). The nice thing about a sump though is that you can actually have all your other equipments (heaters and air stones) in the sump, and this prevents unnecessary cluttering of your display tank. * (5) Sponge filter are the cheapest and easiest to use… but by no means effective in a big display tank. I recommend only using a sponge filter in small tanks (quarantine tanks, hospital tanks, or breeding tanks). The sponge filter is basically a sponge with an airstone underneath. The air passing up the centre of the sponge will draw the water through the sponge, which will act as your main mechanical filtration. There is a certain amount of biological filtration that takes place on the sponge, but not as much as in a biological filter. The nice thing about a sponge filter is that when used in a breeding tank, your fry (baby fish) will actually eat the microscopic organisms off the filter, and thus supplement their diet. They also do not have any pumps on them, so there is no danger of fry being sucked into the filter. There are a few other filters that I have not mentioned, mostly because I do not know them. The under gravel filter is one of the cheapest available, but also the most ineffective. They work on a similar principle to the sponge filter, but instead of drawing the water through a sponge, the water is drawn through the gravel. The mechanical and biological filtration takes place in the gravel, which is not an ideal spot because cleaning becomes a problem. You also would need to take out all the gravel and under gravel filter once every few months to completely clean everything… and you thereby land up having to re-cycle your tank when you reintroduce the water and fish to the tank. One last note to make mention of. The bacteria that live in your filter require oxygen. This is given to them by the continual movement of water over them with the pump being on. During a power failure, this flow of water obviously stops. If the power failure is extensive, the bacteria can and will die off, which will ultimately result in you going through another ammonia and nitrite spike over the next few days as the bacteria re-colonize. During a power failure, the tank can maintain its temperature for a while. The bigger the tank, the better it holds its temperature, as it takes longer for a large volume of water to cool down than a small 30litre tank. I would highly recommend you to invest in a small battery operated air pump for “down time”. When the power goes off, put an air stone under the filter, and let the air bubble through the filter. In the case of an external canister filter or a HOB, you would need to possibly take the biological filter medium out the filter, put it into a bucket of aquarium water, and put the air stone into the bucket. The bucket should then be put into the tank, so that it can maintain its temperature. (A 5litre bucket of water with an air stone going through it will cool off very quickly.) If your budget allows, a better option would be to have a back-up power available purely to run your filter and air pump. (Lights can be left off, as the fish will survive darkness, and unless you have an extremely powerful backup system, a heater will drain the back-up power very fast.) With all this information, I believe you are well set on having an effective filtration system in your tank, as well as knowing what is chemically happening with the water. You should have a fairly good idea now on what type of filter will be best suited for your size tank. My personal opinion is that a sponge filter is better suited for the very small tanks (unplanted). As you go up in size you should be moving towards the HOB or internal Canister. The External Canister’s are great for the bigger tanks, (between 200 and 400litres). I would believe that if you are going anything bigger than a 400litre, you should seriously consider going with a sump. There are many other products available on the market to add to your filters which are also effective means to filtering your tank. I have just covered the basics. There are also many chemicals out there that promise miracles, like clear tanks in 1 hour, Nitrate remover etc. My personal feeling is that in the wild these chemicals are not available, and I would prefer not to be adding chemicals to my tank. When things start going wrong in your tank, it’s a clear indication of filter failure, overstocking or poor maintenance, and I feel that relying on chemical additives to do the work is not the right way to fix it.