Now that you've decided on the fish to keep, the tank set-up has been established, and the location of your aquarium is decided. Finally, the filter you intend to use. 

Everyone knows what a filter is. Perhaps what you may not know is, how you should decide on the filter to use. 

There are 3 main ways of filtration: Mechanical, Chemical, or Biological.

1.	Mechanical Filtration This is the most simple and common method of filtration. A media, like filtering wool, is used to trap dirt and the wool itself is later physically removed from the tank for washing to dislodge the dirt. Most box & corner filters are mechanical filters. The filtering material used must be porous so that water will be able to flow through and the dirt will be trapped within the material. Overtime, as more dirt is trapped, the material will be come "choked". Hence, it is imperative that a certain amount of maintenance is observed. For instance, taking the filter out and cleaning once a week or fortnightly. Laziness will result in the an ineffective filtering system, dirty water, and sometimes, sick fishes. A black or dark coloured filtering material is a good sign that the tank has been neglected.
2.	Chemical Filtration In this method, substances like activated carbon, zeolite, etc., are used to remove the nitrogenous waste like (ammonia, nitrite & nitrate) and other dissolved toxic substances, are removed by adsorption.  Kindly note that some shops sell burnt coconut husk as activated carbon. This type of "carbon" is ineffective. Some people uses charcoal as used in barbecue. This too, is ineffective. For the system to work properly, water must flow through the substance (activated carbon or zeolite, as the case maybe). Just leaving them in one corner of the tank will not be effective. As with the above, the material used must be taken out and washed or re-charged for them to remain effective. Activated carbon should be washed and dried after one month of continuous use. Better still, oven bake it in even heat until it is completely dry. Discard after 3 months. For Zeolite, re-charge with saltwater. Zeolite have a strong affinity for salt and so will adsorb the dissolved salts and "release" whatever it had adsorbed. Therefore, Zeolite should not be used in a Marine Tank or if your water is very hard (high in mineral content).
3.	Biological Filtration Biological Filtration is the process whereby you cultivate bacteria (good bacteria of course) in a suitable medium - gravel, ceramics, etc., - to breakdown the soluble waste in the tank and thus, maintains the balance of your tank. Biological Filtration works by having the nitrogenous bacteria which converts the ammonia and nitrites - present from the fish wastes, excess food, etc. - into a relatively less toxic nitrate, which can then be removed by live plants or by changing water from the lowest point of the tank. Any porous medium with which oxygenated water is able to pass through will automatically have bacteria growing. If your porous medium is not dense enough, not enough bacteria will grow to convert all the wastes. There is no need to introduce or SEED the medium if you can wait. Normally, it takes about 2 - 3 weeks for the bacteria to grow in sufficient quantities to maintain your tank. As with everyone, myself included, 1 week is already a very long time to look at an empty tank. Imagine, 2 weeks? From my experience you can put fishes in after 3 days so long as you do not introduce too many at once. The best is if you can wait at least 1 week. In a planted tank, the waiting period also allows the plants to take root. If you intend to seed the tank, use commercially available DRY POWDERED FORM. As with all life forms kept in a bottle, there is a very short shelf life for those in a liquid form. The dry form is in a domain stage and they only "wake-up" on contact with water. To use a liquid form, you might as well just throw-in a small de-shelled prawn into the tank. Other methods of seeding the tank includes pouring some aged and stable aquarium water (from your friend's tank, for example) into your tank. Some people uses pond water. The best is using "green" water. As mentioned earlier, burying a small de-shelled prawn somewhere in the tank will also encourage the bacteria to grow. Important point to note is that in a bare tank, adding the best bacteria will be of little help. You will need to have a place for them to develop and grow and multiply in sufficient quantities to be of any use. So, be sure to use some medium which they can take root. No Water is bacteria Free. Any water without bacteria, is dead water. Your fishes cannot do well in such an environment. Ceramics

Everyone in the Aquarium Hobby is looking for the ultimate filtering system. The one that works, giving crystal clear water ALL THE TIME, never needs cleaning, and never breaks down. Such a filter does exist. Yes, it does! Yes, you are shocked, such a filter that never needs cleaning does exist. What system? MAID SYSTEM. Get a maid! But when your fishes start dying, don't you dare scold or even blame her.

If you clean your own filters, you will almost always be able to detect some problems before it gets out-of-hand, like over-feeding. You see all the food stuck in the filter system. Perhaps even some strange disc like creatures are found in the filtering wool, smelly water, etc. All these are tell tale signs that something is wrong.

Internal Filters Air Operated These are filters that sit in the tank itself. Besides being unsightly, it takes-up precious space in the aquarium. Most of them use a filtering media of sponge with or without activated carbon or just filtering wool.  At the bottom end of filters, are the Air operated type of filters that come in many different shape and sizes. You use filter wool stuffed into a compartment and water is drawn through the filter wool and up the pipe with the air bubbles (uplift). All their functions are similar. Although effective in its own right, its success is limited to the immediate surrounding area and power of the air pump. As you can guess, the effectiveness is rather limited and depends largely on the air pump itself. These filters are suitable for small aquariums, as most powered types will be too powerful for them.

Powered Internal Filters Powered internal filters almost always use only a sponge. Manufacturers will have you believe that the sponge will grow good bacteria, etc., but such filters can only work as a mechanical filter only. As the surface area is pretty small, it chokes up fast and each time you wash the filter, any bacteria present will killed or be washed away. Forget about using them as a biological system. The principal of operation is the same as the airlift filter box where water is drawn through the filtering media (no matter what it is) and out through a spout. Most effective for free-floating dirt in the water. Change the sponge after about 6 months or if you find the sponge becoming inelastic. Nowadays, these filters are relatively cheap.  Problems with these filters are that each time you remove them to wash, dirt is bound to flow back into the tank. Making your tank looking worse than it does.

External Filters
With external filters the above mentioned problem is eradicated. As with internal filters, there is also powered and non powered. Air powered external filters have very limited effectiveness  They were popular once years ago, and have fallen out of favour since. Mechanical & Chemical Filtration possible.
External Power Filters Very powerful pump output and low wattage but expensive. The large canister allows for different filtering mediums to be used. Mechanical, Chemical & Biological Filtration possible. They canister can be hidden in the fish tank cabinet. A canister is placed outside the tank and water is drawn-in through a pipe into the canister through the filtering media (Filter wool, carbon, etc.), through the motor head and back into the tank. Suitable for large fishes like Goldfishes, Kois, Arrowanas, etc. When you fix your external filters, please check that the pipes are not kinked or the flow will be restricted putting stress on the pumphead. With these filters, you have a large canister for you to put the filtering media of your choice although the manufacturer mostly almost always provides it. All you have are two pipes - An inlet pipe and an output jet pipe or spray - in your tank. These filters are very much more efficient as you can have all 3 types of filtering system present - Mechanical, Chemical, and/or Biological. As the filtering output is very much higher, you also get a better circulation of water.
Overhead Filters  Another type of external power filter is what we call Overhead Power Filter (some call it Gravity Filters). A filter box is place on top of the tank and a power head is used to pump water up into the filter box and the water flows through the filtering media and back into the tank. Personally, I dislike the way the dirty water flows back into the tank whenever the filter wool is removed for cleaning. Most suitable for 24" long tanks only.  Overhead Filters are neat and can be hidden. Design is compact  Good for upto 24” Tank only although 36" models are available. Dirty water tend to drain back when cleaning.  Relatively Cheap

Biological Filters  Just how effective is this and what is it anyway? The most common Biological filter in use is the Undergravel Filter, or sometimes called Sub-sand filter. A porous filtering plate, usually made of plastic, is filled with sand or gravel to about 3" thick. Air bubbles lift water up the airlift tube. Water is forced by natural forces to flow through the gravel/sand, to the undergravel plate, under the filter plate and up to the uplift tube.  Commercially available powerheads can be adapted to fit on the up-lift tube, making it even more effective. For this filter to be most effective, the plate must cover at least 60% of the base. 100% is most ideal. With the gravel or sand acting as the filtering media, your whole tank becomes the filter. The gravel or sand is expected to be dirty over time. What happens here is that bacteria will grow in the gravel or sand and convert the ammonia & nitrites to nitrates (chemical filtration), which can then be removed by the live plants or by water changes. Large dirt particles will be trapped at the lowest point of the gravel and should be constantly removed via weekly/fortnightly or monthly partial water changes. At least once, feed your fish with tubifex worms. Place a small bowl or dish in the tank and place cleaned worms in the dish. Spread a small lot all over the tank (Do NOT OVER DO THIS). The worms will go into the gravel and help keep the gravel from choking-up - just like earthworms in the garden soil. Should they manage to reach the plate, they will be pulled out through the airlift tube and become a nice treat for the fishes.  Important note: the gravel or sand must NOT be coral sand, crush corals, etc., unless your setup is Marine or for Hard Alkaline water fishes.  If you are using crushed corals, as water flows through the sand at a constant rate, it will dissolve part of the coral, and the water will become harder and harder over time. The pH will also increase along with it. For this reason, if you do not intend to change water regularly, DO NOT USE Crush Corals, Shell, or shell grit in your filtering tank. This is the most common problem in large Koi Pond set-up. Because the tank size is huge, water is hardly ever changed. Overtime, the water gets too hard and alkaline and the Kois or Goldfishes become stressed. Tell tale signs will be revealed later when I touch on Preventive Medicine.  After setting up an undergravel filter, your tank water MUST be crystal clear in 12 hours. If not, your filter is not working. Your pump may not be working properly.  Good gravel/pebble size is between 3-5mm. Take a sample of the gravel/sand, place in a glass container, pour vinegar or other forms of acid. If there is strong reaction - effervescence - do not use for acidic fishes. Slight or no reaction. Its OKAY to use.  If you do not intend to use undergravel filter system, it is better not to use any sand/gravel at all.  Advantages of using an undergravel fiter: Cheap & cost effective  Cannot be used if fish digs.  Needs 2 weeks for bacteria to grow.  Gravel type very important.  Can use just an air pump or pumphead. Safe even if there are baby fishes.

MIXED SYSTEM Nowadays, most filters make use of a combination of two or more of these systems. Using a filter wool, activated carbon and ceramics in the filtering chambers is an example of a combination of all 3 systems in action. The problem with any purely biological system is that large dirt particles take a long time to be broken down. So the Best system is one where all three system is at work. Using an external power filter to act as the mechanical and chemical filter while having undergravel to do the biological work. This is very effective for a marine set-up as well. Of course if you have fishes that digs alot, your filter system will go haywire. Either use a larger pebbles or place a filtering wool over the plate.  In a marine set-up, place a thin layer of filtering wool over the plate to prevent fishes or other creatures from exposing the plates. In such set-ups, normally, fine sand is used instead of gravel. The wool will also prevent the finer sand particles from falling through. For small tanks using the box filters, you can modify such filters to be biological filters by simply substituting the wool for freshwater gravel. When water passes through the gravel, bacteria will grow. Because the actual filtering surface area is small, the amount of bacteria that grow will be very limited. That is to say, the efficiency will be limited.

AIR PUMPS You will need at least an Air Pump for your bubbling needs Get the biggest pump if you have a big tank Heavy pumps tend to outlast light pumps Get a small one as spare or for emergency use Get a battery pump (2 battery type) for the odd situations that “Never Happens To Me” Get Air-Tubes of at least 5 meters long Get a metal gang valve Get a few small air stones

Aquascaping simply means the way you decorate your tank.
Assuming you intend to set-up a Community Tank, or Marine Tank, use undergravel Filter and an external power filter. If cash permits, get a powerhead. 

If you are using the undergravel filter, setup the filter first (of course!). 
When setting-up tanks with sand or gravel, fill the tank to about ¼ full with water and gently pour the gravel into the tank spreading over the whole base. The gravel should be high at the back and side sloping to the lowest point where it is the easiest to change water. The lowest point should be 3" high. Overall height – 4-5" behind and side sloping to 3" at the lowest point. Plan for plenty of hiding spaces. Use drift wood, small broken flowerpots, stones stacked-up with holes in between, or even PVC (white) pipes (U shaped) and buried into the sand. Plant heavily, with longer plants at the back and side and large plants like the amazon plants at the centre or off-centre as the main piece. The advantage of having a thick gravel bed is the plant roots will have a better hold. 

With enough resources, you can even set-up fences and have a two-height effect. For such type of setup, do not plant too heavily, as the effect will be lost. 

Ensure that your fishes have at least some clearing for them to swim about, especially in front so that you can see them. Put a small bowl or dish for putting worms in, if you intend feeding them live fishes. 

If you have no intention to use an undergravel filter, paint all 4 sides of the tank with a blue colour or any other dark colour.
Use a flower vase filled with gravel/sand to plant your plant. You cannot be thinking of Aquascaping if you do not intend to use any plant, gravel or sand. 

Make sure of strong lighting for plants to do well. 

Your Tank is now ready. DO NOT put fishes in just yet. Run the tank with the filters, etc., for at least 2 weeks. This is for the bacteria to grow. I know most of you will be putting fishes within 3 days. Be sure that you do not over-crowd them for the first 2 weeks.

pH is the measurement of the water acidity or alkalinity. 4 is acidic and 8 is alkaline. 7.0 is neutral. Normally, water becomes acidic overtime because of fish waste and decaying matter - like food. pH will become alkaline overtime, if you use marine sand, crush corals, shells, corals, marble chips, etc., in your tank of filter systems. Best to keep pH at 6.8 to 7.2. Do not change pH more than 0.2 points at any one time. Changes should be gradual and over time of after a few hours. 

In Singapore context, if your pH is too far extreme, you simply change water. Our tapwater pH and hardness is moderate and is suitable for most freshwater fishes. For the average hobbyist, do not waste money buying the test kits. Test kits usually have a shelf life of only 6 months to 1 year.

pH meters have a longer life span but you must calibrate it occasionally to get accurate readings. Most low end meters, normally needs just one "Calibration Solution" of pH 7.0. Rinse the meter sensor (end tip) first in running tap water and flick gently dry. Insert into the pH 7.0 solution and calibrate as necessary. Some more expensive models will require a calibration of 2 or 3 points, pH 4.0 and 7.0 or pH 10 and 7.0.

For freshwater, pH meters are not essential as you can always just change water. However, if your setup is for marine, or you have a very large tank/pond where changing water is problematic, it is advisable to get one. If you take proper care, the meters will normally last about one to two years. 

In normal circumstances, the tank water gets more acidic with time. Even for marine tanks. Use Sodium Bi-carbonate or Baking Soda, (available at all supermarkets) to make your water more alkaline. Remember not to overdo it -- pH must not fall or rise too fast. To make it more acidic, you will have to use acid like battery water, HCL or Sulphuric Acid. Remember that all these are dangerous to handle and not easy to obtain. 

In olden times, when people build a cement pond, they normally "cure" it by soaking pineapple skins or discards in the pond for a week or two. Well, if you can get some pineapple skin and soak it for a few days, you can try if it works to make your water more acidic. If you are keeping tetras, discus species, etc., you could make use of the peatwater or "blackwater" extract to make your water more conducive for your fishes. 

In a pond set-up, a new pond made from cement, or tiled tends to be more alkaline resulting in extreme pH due to the calcium carbonate. You can use pineapple skin and discards as mentioned to cure it or use get someone to fiber-glass coat it. 

Although in freshwater set-up, doing pH, Nitrite, or Ammonia test is non-essential, in a marine set-up many people will tell you how important such tests are. DO NOT listen to them. If you like doing tests, by all means do so. However, do not be mistaken that YOU MUST DO SUCH TESTS.
Only the pH is most important. As mentioned earlier, your ammonia and nitrite levels are related to your biological filtration and your pH. If your pH is at a constant low, your Ammonia and Nitrite levels will also be present. Under normal circumstances, your Ammonia and Nitrite levels should show no readings. A high NITRATE LEVEL will mean that your bacteria is doing well and they have plenty to feed on. When making water changes, both freshwater and Marine, ALWAYS change from the bottom of the lowest point of the tank. This will remove the nitrates that have built up. Remember: if your pH is very low, your ammonia levels tend to be high.

Fishes normally tell you that they are under stress, or that something is wrong with the water - like the pH is out so that you can check if your filter is choked.
If your pH is very low, your discus becomes very light in colour. If your water is too alkaline, it becomes very dark. So when your fishes suddenly looses its colour or becomes very dark, something is wrong with your tank.  Their eyes turning white or hazy, loss of appetite, nervousness, etc, are signs that something is wroung with your tank.   Although they cannot speak, they do "communicate" with us.

Fishes show symptoms of sickness prior to actually getting sick. So if you solve these problems before they get too serious, you will not have to worry about diseases.

The telltale signs or Symptoms Of Imminent Problems: (this true for almost all the fishes)

Eyes have a white shade	Check pH, pH is probably on the extreme.
Fins clamped or closed	Check water condition & temperature
Fishes looses colour	Insufficient sunlight.
Tails & Fins have a jagged edge	Water too hard or alkaline, check activated carbon
Tails & Fin "blood-shot" esp. Goldfishes	Water condition is not in balance, too much salt and water maybe too hard
Excretion Floats - air trap in excretion	Constipation
Excretion hanging from the fish	Constipation
Fishes become timid, jumpy & nervous suddenly, hiding in the corner all the time	Water too hard or alkaline, too much salt, not enough hiding place, or bullied by others
Yellow residue at the water level	Water too hard, remove crush corals/shells
Fishes becoming very slimy	Too much salt or chemicals used
Fishes float at 30° along surface of water	Chlorine attack, or gills injured by chemicals or internal parasite
Suddenly refuses to eat	Sudden drop in pH, or temperature
Water have a smell	Check filter and replace activated carbon or zeolite
Body have spots, or blotches	Check filter, pH and replace activated carbon or zeolite. Too much salt may have been used; or attacked by other fishes
Fishes rocks its body without moving	Check temperature. Make sure you have a constant water temperature.

COMMON FISH DISEASES 

Tail & Fin Rot	The tail & fins rots away. The edges are jagged like its been bitted by something. In serious cases, the fins and tail are torn or split opened.  If the medication applied is effective, a black outline can be seen along the torn fins.
White spot	Fish body is covered with white pepper-like specks. Very common when temperature drops. This is as common as our common cold. Keep your water temperature constant.
Mouth Fungus	White growth on the mouth. Much like wearing white lipstick but worse as cotton-like growth can sometimes be seen from the wound.
Fish Lice & Anchor Worms (not a disease)	Usually they are introduced into the tank with live foods or plants. Although copper is the main ingredient used in treatment, you can also physically pulled them out with tweezers, and dap the wounds with "RID-ALL" Anti-Fungus.
Fungus	The white cotton-like growth is Not part of the fish fin. It is a secondary fungus infection normally due from injuries like fighting, or rough handling.
Pop Eye	Eyes swell out from its normal place and looks like it is about to pop out.
Swim Bladder Disease	The fish either floats at the water surface or sinks to the bottom when not in motion.
Dropsy	Abdominal area swells up and sometimes the scales protrude out. There is no known effective cure.
Hydra (pest)	This is a pest that may be introduced when you feed live foods. They are a danger to young frys only and post no threat to adult fishes. Click picture on the left for more information.