Set out below are some basic guidelines for looking after your pet goldfish, with simple explanations as to their reasons. They're not foolproof, but should help you to avoid some of the common pitfalls that can occur.

You have purchased an aquarium set-up, which likely includes an aquarium, gravel, internal power filter, water conditioner, flake fish food and a net.

Site the aquarium in a location that does not receive much direct sunlight. Bright areas can cause excessive algae growth as well as temperature fluctuations, which are also harmful to fish.

Wash the gravel thoroughly in a bucket using cold tap water until the water runs clear. If you have a lot of gravel (for instance if you have purchased a larger tank), wash a small amount at a time as it actually cleans more quickly that way. Place a layer of gravel carefully over the bottom of the aquarium, and then proceed to fill the tank with tap water until nearly full. Place the internal power filter in the water, fixing it onto the back or side glass using the suckers provided. At this stage add the required amount of water conditioner, which removes chlorine from the tap water. Chlorine makes the water safe for us to drink, but it is very harmful to aquatic life.

Turn the filter on and over the next couple of days any initial cloudiness will be removed. During this time check that all the equipment is functioning as it should.

After a few days, it will be time to purchase your first fish. It is essential that the tank is stocked very slowly, adding one or two fish at a time. Once you get the fish home, add a quality bacterial starter supplement to the aquarium water to give the filter a kick-start, and float the bag for about half an hour to equalise the temperature before gently releasing the fish. Tempting though it may be to switch on the aquarium light, leave the fish in darkness for a few hours whilst they settle in to their new surroundings.

The filter must be left running 24/7. This is because a colony of friendly bacteria will gradually build up on the filter sponges, and it is these bacteria that break down the fish waste into less harmful end products and keep your fish safe. So it is very important that the filter remains on at all times or these vital bacteria will die. The filter maturation period actually takes several weeks, and during this time it is a good idea to test the water via a test kit to ensure the aquarium filter is cycling properly.

20-25% of the tank water should be changed a couple of times per week in order to dilute the nitrates that are left behind when the filter bacteria process the fish waste. Nitrate, whilst not as deadly as the fish waste itself, can be harmful at high levels, and also causes unsightly algae. So be sure to carry out partial water changes on a regular basis to dilute the nitrate and replenish the tank with some fresh water. Never change all the water at once, as this will kill the filter bacteria. When adding new water to the tank, ensure that it has been treated with a dechlorinator first.

When the aquarium is newly set up and you have added your first fish, only feed them a very small amount, once every two days. Overfeeding, particularly in the early stages when the filter is still maturing, can cause serious problems as there will be too much waste for the filter bacteria to cope with. The fish will be absolutely fine being fed every other day, and offering them too much food will actually do more harm than good.

After about six weeks, the filter should be fully mature. You can increase the feeding to once a day and reduce the water changes to 20-25% once per week. Water changes still need to be carried out, because, as mentioned earlier, the filter bacteria only changes the harmful waste chemicals into less harmful ones - and these still need to be diluted. Also, it is now time to start cleaning the filter sponge, a process that should only be done about once every 6 weeks. Turn off the filter, remove the sponge and give it a squeeze in a bucket of mature aquarium water you have taken from the tank (this can be coincided with a water change). NEVER rinse the sponge under the tap, as the chlorine in the tap water will kill off all the vital bacteria. Sponges do not need to be spotless and it doesn't matter if they are discoloured. The only time they will need replacing is when they don't spring back into shape after squeezing them. And when you do this, replace only HALF the sponge/s at a time, in order to preserve as much beneficial bacteria as possible - never replace all the sponge at once. Cut the sponge in half to do this if need be, then the remaining half can be replaced after a few weeks. Get the filter back up and running as soon as possible after rinsing the sponges, to minimise bacteria loss.

Every now and again, you may need to clean the front glass with an algae pad/algae magnet to optimise viewing. The gravel will need cleaning periodically with a gravel vac too, as this will remove the waste particles that the filter has missed.

If this all sound daunting, don't worry - once you get into the swing of things, there's probably less than an hour's work a month, including water changes, gravel vacuuming, water testing, algae wiping, feeding, and occasionally, some filter maintenance.

Just bear in mind that given ideal water conditions, and provided with enough space (do upgrade the tank as necessary), pet goldfish have been known to grow to more than 30cm/12" long and live for well over 25 years.