Believe it or not, a goldfish should live for 10 to 25 years or longer if it's given the proper care. The Guinness Book of World Records cites a goldfish named Tish that lived 43 years after being won at a fair in England in 1956! Here's how to help your scaly companion survive into the "golden years."

[edit] Steps

Purchase the largest possible tank for your goldfish. While using a 2.5 gallon tank instead of a small bowl will increase longevity, albeit not by much, 10 gallons per fish or more is necessary for quality of life.Choose a tank with a large surface area to increase the amount of oxygen in contact with the surface of the water (i.e., wider is better than taller).
Set up the tank prior to the purchase of fish. Getting it ready may take two or more weeks. It is necessary to build up enough good bacteria to break down the fish's wastes. To do this, do the "Fishless Cycle" (see external links below). Once completed, your Goldfish aquarium will have more than enough bacteria to break down the wastes your fish will produce. Failure to cycle a tank will result in ammonia poisoning.
Provide mental and physical stimulation for the fish. Decorate the tank with gravel, bridges, plants, etc. Gravel provides a place for good bacteria to grow, and goldfish like to hide and swim through little buildings and bridges. Rearrange the bridges and plants on a monthly basis to offer the goldfish "new" areas to explore.
Add a filter. Either a large internal or an external is best, as goldfish are very messy creatures. Without a filter, smaller tanks will foul and become deadly in just a day or two. Keep in mind that having a filter doesn't mean you can avoid cleaning the tank. Even with a filter, change 20% to 50% of the water about once every week.
Add some equipment to increase oxygen diffusion into the water. A powerhead is best, although some fancies will not like the current. If this is the case, a small air pump and air stone is sufficient.
Clean the tank at least once a month, but more frequently is preferable due to the large amount of waste goldfish produce. This is essential. How often you do this will depend on the size of your tank, the number of fish, and the effectiveness of the filter.
- When you add/change water, use a dechlorinator that also removes chloramine and heavy metals as per instructions.
- Frequently test for ammonia and nitrite. A pH test is also handy to ensure your goldfish's water is not too alkaline or acidic. This can be purchased at any pet store. Do not modify the fish's water, however, unless it is significantly different from neutral. Goldfish can tolerate a wide pH range, and pH modifying chemicals are not a lasting solution without more consistent monitoring than most people will do. A range of pH 6.5-8.25 is fine. Many municipal water supplies buffer their water up to around 7.5, and goldfish will live very happily in this range.
- Do not remove the goldfish during a water change. Using a gravel vacuum to suck debris out of the gravel can be done with the fish in the tank. Frequent partial water changes are better than full (and stressful) water changes.
- If you do need to catch your fish, consider using a plastic container rather than a net, as the fish can injure its fins and scales while thrashing around. This also increases stress! If a net is the only option, soak it prior to use. Dry nets are much more likely to cause injury than wet ones.
Allow the water temperature to change as the seasons change. While goldfish don't like temperatures over 75°F (24°C), they do seem to like seasonal variations where the temperature falls to the high 50s or 60s (15-20°c) in the winter. Fancier goldfish are an exception and cannot easily tolerate temperatures below about 60°F (16°c). Be aware that goldfish will not eat below 50-55°F (10-14°c).
Feed the goldfish once or twice daily with food specifically designed for goldfish. If you choose to feed them twice, then reduce the size of the meals. Give them only as much as they can eat in a few minutes, and clean any leftovers immediately. If a floating food is used, soak it in water for a few seconds before feeding so that it will sink. This reduces the amount of air the fish swallows while eating, which in turn reduces the risk of flotation problems.

[edit] Tips

Be sure to regularly clean leftover food and waste from the gravel. You can do this by using a siphon.
If the air pump is too strong for the size of the tank, you may place a clip or commercially available valve on the tubing and reduce the amount of bubbles.
Never use a tank under ten gallons unless it is temporary (i.e. less than a week). Anything smaller will stunt the fish leading to many health problems, and can be considered cruel.
Carbon is a valuable component of filtration IF it is replaced monthly.
Goldfish can grow to be over 12 inches long if put in tanks or ponds that are large enough! However, contrary to popular belief, fish do not stay the size of their tank. Do not purchase a too small tank and expect the fish to stay that size.
Test your water for pH, hardness, and alkalinity initially. If your water is soft, adding some oyster shells to a mesh bag is good as it can help raise the hardness and buffer the water. Goldfish like water with a pH of 7 to 8 and moderate hardness.
Many people use aquarium salt with goldfish, however, this is usually unnecessary.
Test the levels of Nitrite and Ammonia regularly. Ammonia and nitrite are very poisonous and any level over 0 PPM is bad. If the readings are above 0 PPM check more frequently and do more frequent water changes. Nitrate is tolerated up to levels of about 40 PPM. You should be able to get more detailed info about your particular goldfish's tolerance for these chemicals from any good pet store.

[edit] Warnings

Avoid using gravel that is sharp or of such size as the fish can get it stuck in their mouths. "Pea" gravel or sand works best.
Be careful when adding multiple goldfish to the same tank, as they can spread diseases. When at the pet store, check to make sure the fish looks healthy. If there is an abnormal number of dead fish, then use caution when buying. New fish should be quarantined away from the old fish to reduce the spreading of parasites, bacteria, and/or fungus.
If you are worried about the quality of the tap water in your area, call your local pet store and ask if the water is usable for fish. Your local government should be able to give you a water quality report if you have city water. This report will give you an idea of the local water chemistry.
Be sure there is no soap or detergent residue in the container used for water changes. This is poisonous to fish.
Water heaters are prone to malfunctioning and can stay on even after they are set to turn off, so monitor them with a thermometer. Most modern heaters work well and should not malfunction.
Be careful when transporting your goldfish. Stress can reduce the lifespan of a goldfish.
Get a top or lid for the tank so your goldfish cannot jump out.
Many cities put chloramine in water rather than chlorine. Chloramine does not evaporate and must be removed by adding an additional chemical. Check the label of your dechlorinator to ensure that it also removes chloramine.
Temperature fluctuation will stress goldfish - try to keep the temperature as constant as possible.
It is unhealthy to overfeed your fish. Only feed your fish as much as directed.
Remember that some goldfish cannot be kept with other goldfish. For example, Comets will eat all the food before fancy goldfish can get to it.