By Chris Merrell
Owner of 21st Century Fish mailing list


So you're thinking about getting a fish tank so you can watch the little blighters swim about and perform their cute antics?  OK.  No problem.  But before you do please take some time and read through this document as it will save you time, money and sanity.  After all once you start keeping fish you want to keep them alive and happy right?

The purpose of this document is to give you some knowledge to help you decide on what it is you require.  This is by no means a highly detailed explanation about fish keeping, but rather an explanation about some of the pitfalls beginners will encounter when they first start off.  I'm an amateur hobbyist and I am still learning about my scaly friends.  I just want to give you a basic knowledge to help you have a trouble free start to what is a fascinating pastime.

The main thing to do before you even start considering getting a tank  (and I can't stress this enough)  is to research, research & more research.  There is a wealth of knowledge available via the internet, petshops, libraries etc.  The more you know about aquariums the better prepared you'll be when something goes wrong  (and believe me it will go wrong).

The things you have to consider are as follows :

Types of fish
Tank size

Lets discuss these in sequence


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OK.  You happened to be looking around the fish section of your local petshop and you see these really cute fish.  And in the next tank you see another species you like too.  You just got to get them, right?

Well hold your horses.  What you have to consider is that one is a cold water type and another is a tropical type and very aggressive  (for instance).  The common misconception is that all fish swim in water  (which they do)  and that you can keep them in a gold fish bowl  (not true at all).  This has led to many people just buying any old piece of kit  (of which I shall be getting to later)  and becoming frustrated when all their expensive  (yes,  most fish are quite dear these days)  fish end up visiting The Big Toilet In The Sky.  This can understandably put people off and they end up dumping their kit at a fraction of the cost they originally made.  Not a good way to go about it don't you think?


So what types of fish are there?  Well, these can be split into categories - Cold freshwater, tropical freshwater and marine saltwater.

Cold freshwater - These are typically goldfish, koi carp  (glorified and expensive goldfish),  shubunkins etc.  Like the name suggests you don't require the tank/pond to be heated.  Most of this type of fish will grow quite large and so need a lot of room to move around in.

Tropical freshwater - This is the most diverse type of fish, and also the most commonly kept in aquariums.  Some of the fish you can get are tetra  (close relation of piranha), guppies, mollies, angelfish etc.  These fish can be small  (about 1 inch), but can grow to 9 inches or larger.  They are called tropical because they need water that is kept at quite warm levels  (typically about 26 degrees)  and mainly can be found around the equator.

Marine saltwater - This is the hardest type of fish to keep because you have to monitor the salt levels in the water constantly.  A slight deviation and your fish could become ill or even die.  These are fish you can find in the sea, such as sea horses and sea cucumbers.  Also you could setup a coral colony too.  While this type of setup would look stunning it requires major cash funds, lots of patience and a very deep commitment to maintaining the environment.

The above is just a small example to help you choose what type of tank setup you require.  Another thing to be careful of is species compatibility.  By this I mean how different species of fish of the same type interact with each other.  Take angelfish and neon tetra for example.  Both are really nice looking tropical fish.  Both are placid  (on the whole).  But put them in a tank together and by morning you'll have fat looking angelfish and you'll be wondering where all your neons have gone.  The explanation is that in the natural environment for these fish, neon tetra is the angel fishs staple diet.  As you can imagine you wouldn't want this.  This can even occur with subspecies of fish.  You can get apparently docile fish who will then start getting aggressive and territorial.  To avoid this you need to ask questions, research and trust that you don't get argumentative fish :)


Some consideration has to be given to breeding.  Neon tetra are very hard to breed.  Guppies on the other hand just need you to look at them and they become pregnant.  It's fascinating to watch fry coming into this world, but beware that they will most likely be eaten by their mother or other fish if steps aren't taken.  This can be in the form of a breeding trap where the female will give birth in one part of the trap which has gaps for the fry to escape into a second part.

Feeling hungry?  Well like us fish can be vegetarian, carnivorous or omnivorous.  Pleccostomus are vegetarian and love cucumber.  Samurai fighters are carnivores and like nothing better than to gulp down bloodworms.  Golden barbs will eat anything as long as it moves.



Careful consideration must be given to the placement of your tank.  The temptation is to place it in a prominent location.  There is nothing wrong with this so long as you follow these Do's & Don'ts DO -
* Make sure that the surface where the tank will reside is flat, even and can support such a heavy weight
* Place the tank where it is easily within reach for maintenance.
* Have a cover over the tank to stop dust, mobile phones and stray pets from falling into the water.
* Make sure you have an adequate amount of electrical sockets close to the tank.
* Persuade people not to tap the tank as this upsets the fish.

* Place the tank on or near anything that vibrates or makes loud noise.
* Place the tank where it can be knocked or bumped into.
* Allow direct sunlight to fall on the tank. This will encourage rapid algae growth.
* Place the tank where water can damage the area on which or around where the tank sits.  Also be aware of the danger of mixing water with electricity.

With these simple pointers you and your fish will&  (probably)  have a happy and content existence in a safe and easily maintained environment.


And now it starts getting interesting  (also complicated).  In order not to confuse matters or myself, the tank section will be broken down into several sections.


You can find tanks in all shapes and sizes.  These can range from the typical glass/plastic goldfish bowl, through custom made "fish walls" and all the way up to the monster tanks you can find in oceanic institutes.  But lets keep it simple for the purposes of this document OK?

While talking with other aquarium keepers you may hear them referring to "30 long" or "55 tall".  This is in reference to the basic size and shape of their tank.  30 long means it is a 30 gallon tank that is elongated.  The same thing for 55 tall, 55 gallon and taller than it is wide.  There are many different dimensions of tank, tall, long, deep etc.

The important thing to remember is to plan ahead and think about the space you have available to locate your tank in.


OK,  so you got the perfect tank and the perfect location.  You now need to think about what will actually go into the tank.  The most import feature for any tank is filtration.  Before I go into the different types of filters I'll give a brief description about why it is important.

In the wild the bio-cycle is taken care of naturally.  Water flows, waste products are diluted and taken away etc.  But in an aquarium you have a closed environment and without water flow, filtration and water changes waste products from the fish will quickly turn the water into a stagnant mess in which nothing can live.  Remember that fish excrete their own body weight in waste products each day.

The bio-cycle is pretty simple but highly important to water quality. In "cycled" water there are numerous bacteria which will settle on a surface and start to colonise and also convert waste products into less harmful chemicals.  The cycle starts with ammonia which is the main waste product from fish.  The bacteria converts this ammonia into nitrates which in turn gets turned into nitrites by different bacteria.  This final waste product, nitrite, will then be removed by dilution when you do a partial water change.  If you are wondering how this bacteria gets into the tank in the first place it is because the fish themselves excrete the bacteria that breakdown their waste products.  Nice and convenient :)

Now you have a basic understanding of the bio-cycle and why it is important we can now move onto filtration proper.

Filters come in several flavours, these are the ones you are most likely to use.

Air powered filter :  This type of filter typically has a sponge or carbon granule filter head.  Water is drawn through the filter head by displacement caused by air bubbles.  The bubbles  (normally from a small air stone)  push water up a tube and so pulls water back in through the filter head.  This is a very simple kind of filter, but not very effective for moving large amounts of water.

Mechanical filter:   Electrically powered internal tank filter.  A magnetic impellor is used to pump water through the filter.  This arrangement consists of a sponge/padding material, carbon granule pack, water and air flow tubes.  These are commonly known as powerheads.  This is quite an efficient filtering method.  Bacteria colonies essential for the bio-cycle build up in the sponge/padding, while the carbon granules filter out the larger particles in the water.  Water is aerated by drawing air into the water flow.  It can also move lots of water volume in a short space of time.

External filter:   This is essentially the same as a powerhead mechanical filter.  The important difference is that the unit is outside the tank and through tubes it takes away dirty water and puts back clean water.  These are easier to maintain than internal filters.

Undergravel filter:   As the name suggests this type of filter uses the aquariums gravel as a filter medium.  This is achieved by a plate with slots or holes which sits underneath the gravel.  Water is drawn through the gravel and the undergravel plate into an uplift tube.  This can be achieved with either an air displacement method, or a powerhead mechanical pump.  Once uplifted the water is aerated and allowed back into the tank.

This is a highly efficient way of filtering your aquarium due to the large surface area available for filtration, and for the bacteria colonies.

A slight variation on UG filters is the reverse flow method.  Water is pulled into the powerhead  (air displacement wont work with this)  and pushed down the uplift tube, and pushed back into the tank through the gravel plate and then the gravel.  On the powerhead you would have some kind of filter medium to trap particulate matter.  This has the added advantage of cleaning the gravel of excess food and fish poop.


This is essential for tropical tank setups.  Due to the nature of the tropical fish they require warm water to live in.  The typical temperature is normally around 26 degrees, but depending on what fish species you have they may require cooler or warmer temperatures.

The heater itself is very basically a thermostatically controlled heating element encased in glass.  You can set the temperature and it will maintain this temperature, by turning itself on and off.  It does this in a similar way to automatic electric kettles which shut off when the water has reached boiling point  (I could explain how this happens but its not terribly interesting).

Depending on the size of tank you have chosen dictates the size of heater you will need, or indeed how many if you have a massive tank.  The key thing as always is research.


While its not essential to have a lighted tank it does make things more bearable for the fish.  Its also nice if you can see where the little blighters are. :)

The commonest form of tank lighting is the hood light.  This is a fluorescent light placed in the hood cover of the tank, and through a glass panel shines down into the tank.  Hood lights come with a control box that has the starter capacitor and on/off switch.  The amount of time that light is required varies from species to species and controlling it can be a chore.  The easy way to control the lighting is to get an electrical timer switch.  Once you have programmed the timer and plugged the light into it you dont need to keep turning the light on and off manually.

You can also purchase special fluorescent tubes that give out different shades of colours to make you fishs colouration more predominant.  These types of fluorescent tubes are called beauty lights.


This is the really cool bit about aquariums.  Apart from gravel you can place allsorts of ornaments and even live plants inside you tank.  You local fish store will have a display of things like castles, skulls and stupid  (sorry cute)  looking fish in a deckchair with a sign saying no fishing.

It doesnt stop there.  You can also get air toys, like a drinking skeleton, or a large oyster that opens occasionally, and even a scuba diver that falls and rises in the water.  Airtoys are powered by aquarium air pumps.  Air is fed from the pump via a rubber tube to the airtoy.  You can have more than one airtoy and control them with an air tap arrangement.  If you plan to use airtoys remember to fit a non return valve because you dont want water to seep back into the pump when you turn it off.

Another type of ornament Ive seen recently is a lighthouse that has a laser beam for a light.  You can also get different add-ons for different effects.  From what Ive seen it looks pretty stunning.

Some species of fish love to hide and so having an ornament for them to hide in would be nice.  You dont even need shop bought ornaments. You can use slates, stones and driftwood.  Really speaking just about anything can be used as an ornament as long as it won't rot, or contaminate the tank or fish.



Now that you have set your tank up with an efficient filtration method and heated it to the desired temperature and made it pretty for your chosen types of fish thats all you have to do right?  Nope . Sorry.  More to it than that.  Let me explain.

Your tank is full of water and the filter is running.  Everything looks dazzling and crystal clear.  The problem is the water is technically sterile.  In other words it has no bacteria to start the bio-cycle process.  Beginners often make this mistake and it even has a name.  Its called new tank syndrome.  So how do you solve this problem? 
There are two methods you can use.

Method one:   Get some cheap and hardy fish like goldfish  (for cold water),  or guppies  (for tropical).  Place them in the tank and leave them to mature the water for about one week.

Method two   essentially the same as method one except that you use a trizyme additive to boost the bio-cycle.  This has the added benefit of shortening the maturation process considerably and is a lot safer for your fish.


This is the most important task for an aquarium keeper.  Constant monitoring of the water quality will help keep your tank and fish in harmony.  You need to measure the PH levels  (acid/alkaline content),  ammonia levels, nitrate and nitrite levels, chlorine, water softness/hardness and salt content.  Dont panic as you dont have to be a PHD chemistry student or set up a mad professors lab.  You can get water testing kits at your local fish store.

Another thing to bear in mind is dilution of waste products.  Remember I mentioned that the bio-cycle starts with ammonia, which is very harmful to fish, turns that into nitrate  (not as harmful but still pretty nasty), then finally into nitrite which, in large quantities, can be damaging to your fish.  You dilute these waste products by performing a partial water change  (i.e. Remove dirty water and replace with clean water).  This is a constant topic of hot debate and no one person can give a definitive answer on the amount of water to change.  The average consensus is a volume between 25% and 50% of your tanks total volume.  If you have larger fish  (they produce more waste)  you will have to change the water more often.  It is also important that before you do a water change that you let the water you are going put back into the tank stand for around 24 hours.  This allows the water to a ttain room temperature and any salt/chlorine to separate into the bottom of the container.  You may also add some kind of treatment at this point.


You've noticed that some of your water levels are not quite right, so what can you do?  As the saying goes   Prevention is better than cure.

There are many kinds of chemicals and additives to control your water quality.  So many that I can't possibly list them all, but here are few I will recommend for their usefulness.

Trizyme:   I've already motioned this above.  Its actually a type of yeast that makes bacteria to help start the bio-cycle.

Aquarium tonic salt:  This provides a salt content to your water and helps keep your fish happy and healthy.  It also provides a PH buffer that absorbs sudden changes in the waters PH levels.

Stress coat:  Try to get it with aloe vera added to it.  This encourages and maintains the fishs natural mucus membrane that it has over its body.  This membrane protects the fish from disease.  The aloe vera also helps calm the fish when it is distressed.

Filter aid :  This is actually a clumping agent and is used to fuse bacterial blooms together so that the filter can absorb them more easily.


While you may follow all the above guidelines it is still inevitable that you will get sick fish.  There are many types of illness that can affect your fish.  These can be internal parasites, fin rot, white spot and swim bladder problems to name just a few.  I wont go into disease diagnoses, cause and treatment, as that is a large document in itself.  I will say however that help is never far away and more often than not it is fairly simple to cure.  Your local fish store will have a range of medications to treat whatever ails your fish.

This scenario will become familiar to you after some time of keeping fish Its feeding time and you pop the lid on your tank ready to drop some food in.  You see something float past that looks like a furry fish shape.  This is infact a dead fish that has fungus growing on it.  As with all dead fish you have to remove them immediately in order not to pollute the water.  Dead fish are a breeding ground for harmful organisms and fungus.  Its always sad to lose one fish and really annoying to lose a whole tank full.


Talking of food it may interest you to know that most fish will eat and eat until they choke and die.  When thinking about a feeding regime you need to know the fishs diet.  How often to feed depends on the species.  As a rule of thumb I give my fish a little food twice a day.  Now the next bit may sound callous, but believe me when I say youll get healthier fish.  Pick one day in the week and dont feed the fish on that day every week.  Let me explain.

Fish, in their natural environment, are scavengers.  They are constantly looking for food.  In a fish tank they have room service and so get lazy and lethargic.  By skipping a feeding day they will start scavenging in the tank.  This has the added bonus that any uneaten food leftover from the last feed will most likely be eaten on the skip day and so keep your tank a little cleaner.

Well that about sums up the basics of aquarium keeping and I hope you find this document useful and informative.  When I first started writing this I thought it would be quite short and maybe I would have to have help from my friends on the TFCF mailing list.  As it turns out I knew more than what I thought.  I am quite shocked about this, but in a pleasant way.  Look out for other guides from 21st Century Fish and maybe you would like to join us.  The link to do so is at the top of this guide.  Until next time take care people.

Chris Merrell


RIYAN Productions