Aquariums are popular decorative features in homes, offices, and even restaurants. They can be beautiful facsimiles of exotic underwater environments, such as the Amazon River or the Great Barrier Reef. And besides being fascinating to look at, aquariums provide a tranquilizing element in a world filled with stress. But before you decide to add an aquarium to your home or office, you should learn as much as possible about their care and maintenance.

Most people who have aquariums--or aquarists, as they are known--keep tropical (warm-water) fish, such as angelfish, rather than cold-water fish, such as goldfish. That is because tropicals are generally more colorful and exotic-looking than cold-water fish.

There are two basic types of tropical fish aquariums, freshwater and saltwater. Most experts advise against starting with a saltwater aquarium, because it is more expensive to set up and stock and more difficult to care for than a freshwater aquarium. If you begin with a freshwater aquarium, you can use most of the same equipment later if you decide to switch to a saltwater setup.

The first thing to consider is the size of the aquarium you want. If you are trying to fill a specific location in your home, you will have to buy what fits best in that spot. To get some advance idea of the size aquarium you need, keep in mind that one of the most common 76-liter (20-gallon) rectangular tanks has proportions of about 60 centimeters long by 30 centimeters wide by 40 centimeters high (24 x 12 x 16 inches).

If space is not an issue, buy the biggest tank you can afford--at least 76 liters. You may be tempted by inexpensive 38-liter (10-gallon) starter aquariums available in many pet stores. But these usually come with inferior equipment and do not offer enough room for even a small number of fish, and certainly not for the variety of fish you are likely to want.

When selecting a tank, keep in mind that the larger it is, the heavier it will be when it is full and operating. A liter (0.26 gallon) of water weighs 1 kilogram (2.2 pounds). So, a 76-liter aquarium, once filled, weighs more than 76 kilograms (170 pounds), counting its own weight and the weight of anything in it heavier than water. It is important to consider such great weights when deciding where to place your aquarium. You might want to buy a special stand for it. Some stands are made of black wrought iron, and others are specially constructed wood cabinets.