Even if it has nothing more than a few goldfish, a well-lit aquarium bubbling away in a corner adds a soothing touch to any room.
A rectangular glass tank is the best container. Allow 50 square inches of water surface for each fish, and at least a gallon of water for each inch of fish. Thus, if you have two fish, each about 2 inches long, you need a 4-gallon tank with an opening of 100 square inches. Actually, 4 gallons is quite small and you'll probably want a much larger tank.
Make sure the tank is on a sturdy, level surface. Place it where it will receive diffuse light; keep it out of direct sunlight and away from drafts. Buy an aquarium cover with a built-in fluorescent light. This keeps dirt out of water, minimizes evaporation and helps maintain an even water temperature. Sudden changes in water temperature can be fatal to tropical fish. To avoid that, equip your tank with a thermometer and water heater to maintain a constant temperature between 70 and 80 degrees.
A day or so before you buy pet fish, wash the tank with clear water. Cover the bottom with 1 1/2 to 3 inches of well-rinsed aquarium sand or gravel. Slope the sand or gravel to form a slight hollow in the middle--it will catch dirt that can then be removed.
Plants are important to an aquarium. Live plants, such as Amazon sword and Java fern and elodea, absorb chemical waste products in the aquarium that can be toxic to fish.
Soak the plants for 15 to 20 minutes in a solution of 3 tablespoons of salt per gallon of water to get rid of parasites. Then, rinse them in clear water and embed them in the sand or gravel.
Plants also absorb carbon dioxide and give off oxygen during the day. At night, however, they use up dissolved oxygen, so install an air pump with a filter to ensure proper oxygenation of the water.
Fill the tank with tap water. Let the tank stand, uncovered, for at least 24 hours.
For a first aquarium, choose freshwater fish, which are easy to maintain. Try a mix of nonaggressive tropical fish, such as guppies, tetras, barbs, small catfish and swordtails. Select fish that appear lively, well-fed and free of fungus and other growths.
When you add fish to the tank, float them in their plastic carrying bag for five to 10 minutes to allow water temperatures to equalize. Now open the bag and add tank water until the water volume doubles in the bag. Wait another five minutes, then gently net the fish out of the bag and place them in your tank.
Never pour store water from the bag into the tank; it contains waste products that will pollute your aquarium.
Overfeeding is a common error. Establish a feeding time and stick to it. Feed your fish twice a day with commercial fish food. Drop a small amount into the tank. If the fish consume all of it within five minutes and continue to come to the surface looking for more, add another pinch.
Weekly maintenance includes scraping algae from the sides of the tank with a long-handled glass scraper. Remove plant trimmings, dead leaves, sediment and uneaten food with a dip tube. Both tools can be purchased at a pet shop. Siphon off as much as a third of the water from the bottom of the tank every week, replacing it with tap water that has been sitting for at least 24 hours.