A:

First, goldfish require the proper water environment.  They are freshwater temperate fish, so they are happiest in an environment that closely resembles a pond.  The water should be chlorine-free and kept between 65-72 degress Fahrenheit. They also grow fast and produce more waste per individual than many other fish species, so the larger the tank and the fewer the fish in the tank, the better. 

Therefore, rather than housing two or three goldfish in a tabletop fishbowl, the fish will thrive in a ten-gallon aquarium filled with tap water that has been conditioned with a commercial dechlorinator, and heated to maintain about 70 degrees Fahrenheit.

The longevity of the fish also will be enhanced by adding a mechanical filter to the system.  In this way, toxic waste products produced by the fish will be converted to non-toxic materials that will leave the fish unharmed.  One of the most common causes for early tank failure is "new tank syndrome" in which several fish are placed in an aquarium or fishbowl which has inadequate filtration.  Over the first few weeks of operation, the fish produce ammonia-type wastes that are not converted to less-toxic nitrates because there are insufficient beneficial bacteria present in the filter to effect that important transformation.  Hence, the fish are exposed to higher and higher concentrations of toxic ammonia, and eventually die. 

Often, owners report that the water became cloudy and the fish died.  If the fish are kept in a tabletop fishbowl, there is no filtration available, so the fish are poisoned by increasing levels of their own toxic waste. Fishbowls are "death chambers" for goldfish.  This is classic "new tank syndrome" and can be avoided by following a few basic rules:

 - Begin with as large a tank as is practical and install a filter appropriate to the tank size.
 - Heat and condition the water.
 - Stock the tank with only one or two fish for the first three weeks of operation.  
 - Feed sparingly once or twice a day.
 - Feed only as much as the fish can eat in five minutes.  Any extra will contribute to the waste product load that can overwhelm the filter's ability to detoxify waste and also result in the dreaded "new tank syndrome". 
 - Stock fish, which are compatible.
 - Siphon off 25% of the tank water and replace it with fresh dechlorinated water every two weeks. 

With this small population size, the filter will not be overwhelmed and is able to convert waste products to non-toxic forms more effectively.  In terms of compatability, goldfish should live only with goldfish, not with tropical fish or saltwater fish or catfish. Improper mixtures of fish result in fish death, which is not only disappointing to the fish keeper, but fouls the water. 

A good water conditioner is Stress-Coat which dechlorinates and adds a soothing slippery coating to the fish which they appreciate.  Cover your fish tank. Fish can jump out of an uncovered tank and will die on the floor.  It is lovely to have a fish tank with a matching glass cover and fluorescent light fixture to illuminate the fish. Turn off the light for at least eight hours each night.  The fish do not like constant light.

For those goldfish keepers that desire the make an aquarium truly special, plastic plants or rocks or interesting ornaments may be added to the tank.  Also, goldfish are great fans of green vegetables and particularly enjoy two or three cooked green peas with the skins removed.  This food provides excellent roughage in the diet and contains pigments to enhance the color of the fish. 

A common complaint from goldfish owners who have the fancy, round-bodied goldfish is that periodically the fish have difficulty maintaining their place in the water column and repeatedly float to the top of the tank.  Subsequently, they have to struggle to swim underwater again.  This is called "floating disease" and is a direct result of the unusual body shape and the inability to process gas in the digestive tract so that normal swimming is disturbed. 

The best way to avoid this problem is to feed only a sinking pellet diet to these fish so they gulp less air when they eat.  The cooked peas added to the diet add roughage to aid digestion and reduce the gas buildup that causes the troublesome floating.

An excellent resource for the aquarium-minded individual is:
 
The Complete Fishkeeper: Everything Aquarium Fishes Need to Stay Happy, Healthy, and Alive by Joseph S. Levine, William Morrow and Company, Inc., New York, 1991.