Fish are relaxing and beautiful to look at and a well-kept aquarium is a delight to the eye.

Never keep fish in a round glass bowl, as the mouth of these bowls is comparatively small and only a limited water surface is in contact with the air. This can result in lack of oxygen and dead fish.

Fish are gregarious by nature, so always keep more than one, but do not overcrowd the tank and do not keep incompatible fish together. Some species are carnivorous and may attack, or even eat, the other fish. Contact your local Aquarium Society for advice.

People keeping fish for the first time would be well advised to begin with inexpensive coldwater fish, such as a few hardy goldfish, as they are easier for the novice to care for. A tropical aquarium should be set up only after having experience and success with the maintenance of a coldwater aquarium.

The Tank

An aquarium about 60 × 30 × 30cm will take about 10 small fish and two water snails. A good rule of thumb is to allow 30cm² of surface area to every 2cm of fish, including the tail. An average fish will need 5 litres of water for each centimetre of body length. The fish capacity of the tank will be increased if it is artificially aerated.

Setting up the aquarium

  1. Place the empty aquarium on a flat solid surface. Remember that 1 litre of water weighs 1kg and you must add the weight of the tank and the equipment, so be sure the surface on which you place the tank will be able to support the weight.
  2. Half fill the aquarium with water, place sand or pebbles on the bottom, anchor in some water plants by placing pebbles or small rocks on their roots, and fill with water to within 5 centimetres from the top of the aquarium. Leave it to season for a few days before buying your fish. Chlorine in the water will kill fish so it is important to allow time for it to evaporate. Alternatively, the chlorine may be neutralised by the use of special tablets or water ager available from your pet store or chemist.
  3. A water filter operated by a small electric motor will help to keep the tank clean, but is not essential for coldwater fish. However, algae will still overgrow in the tank if the fish are overfed or the tank is badly positioned.
  4. The same motor can operate an aerator that pumps tiny bubbles of air into the water, providing more oxygen. This is necessary only if you have more than the recommended number of fish in your tank.
  5. For tropical fish a heater, thermostat and thermometer are also needed to keep the water at the right temperature.

Sudden changes of temperature often kill fish. If brought from the shop in a plastic bag, put the bag complete with fish into the tank for an hour before releasing the fish.

Fresh water should be added to the tank when needed, to make up for evaporation. If water in the tank becomes obviously discoloured, it should be changed.

Changing the water

The use of a glass syphon tube and hose will facilitate cleaning. Syphon out about 1/3rd of the water. Get the tube right down into the gravel, work it across the bottom of the tank, and allow the water to run into a bucket. Never undertake a complete water change.

Replace with clean, fresh water that has been allowed to stand at room temperature for 24 hours so the chlorine has evaporated. (Better still, collect rainwater and use this).


Do not overfeed your fish as this can kill them, and uneaten food decomposes in the tank. Feed lightly once a day using special food available from pet shops or supermarkets. Occasionally, give a chopped earthworm to prevent constipation.


Overcrowding and polluted water are the principle causes of death in aquarium fish. It is important that the tank is cleaned regularly to remove excreta and excess food, which will foul the water.

Gasping is a sure indication of a fouled tank. Other signs of infection and disease are: fluffy white patches or spots; a general mouldy look with loss of colouration; a rotting tail. These diseases can be fatal, so seek professional advice should they occur. Fish can also get worms and should be treated annually.

A Few Important Reminders

Don’t put the tank in direct sunlight.
Don’t top up your tank with cold water straight from the tap.
Don’t bang on the glass. Fish are upset by vibrations.

Remember that household sprays, such as insecticides, can pollute the aquarium and kill the fish. Always cover the aquarium before spraying.

Alternatives to the Tank

There are other ways to keep non-tropical fish and you may prefer to consider them.

  1. You could buy a fibreglass pond
  2. You could sink a paddling pool into the ground.
  3. A hole can be dug in the ground and lined with heavy-duty polythene. The pool should be shallow at one end, gradually deepening toward the other end.

Adequate aquatic plants must be placed in the pond to help oxygenate the water and to provide a shade and shelter for the fish, as well as a place for fish to lay their eggs. Rocks also provide good shelter for fish and are decorative. A water filter system is necessary to remove algae and other impurities.


The ordinary goldfish can live for up to 25 years in a natural pond environment, but their lifespan is much shorter when they live in an aquarium.