Determining what proper goldfish tanks should be like is every bit as important as determining what proper tropical fish tanks should be like. We often think of tropical fish as requiring special care, and that's true. It's also true that goldfish, if they are to remain healthy and live out their normal life spans, require their own special care.
Goldfish are often thought of as being short-lived fish. That is simply not true, as a goldfish typically has a life span in excess of 10 years. What is true is that when placed in something other than a proper tank, like a goldfish bowl, a goldfish may indeed be short lived. A goldfish in a small bowl is unlikely to live for 10 years. Blame it on the small bowl, or the goldfish's owner if you will. For one thing, because of its shape, the goldfish bowl does not provide a large water surface area, necessary in keeping the oxygen content in the water at a required level. In addition, a single goldfish requires quite a bit of water, about 20 gallons to be exact. You will not find many 20-gallon goldfish bowls on the market and, if you have two goldfish, you'd better be looking at a 30-gallon bowl. An aquarium style container is definitely what you need, unless of course you are going to keep the fish in an outdoor pond.
Even inexpensive common goldfish can be extremely attractive to look at, and deserve to be placed in an environment where they will thrive. Their availability and low cost should not diminish from their value as pets, and as ornamental fish. Some types, especially the more common types, can become quite large over time, require plenty of room to roam, plus they will create quite a bit of waste. A 20 gallon tank for one fish is really the absolute minimum size that should be considered. Get a 55 gallon tank and 3 or 4 goldfish, and you can then sit back and enjoy watching them.
Of course goldfish tanks holding only goldfish and water are not much to look at, and are not good for the goldfish either. Since the goldfish is a cold water fish, you do not usually need to worry about installing a water heater. You do need to install an air pump to provide oxygen, and a filter to keep the water clean enough for the fish. You should also consider plenty of plant life, not only for appearance, and as a secondary though minor source of fish food, but also because plants can also assist in the filtering process. Goldfish are usually very fond of eating plants however, so plan on having to replace plants fairly often.
To keep the water at a sufficient quality you'll want to be changing some out on a weekly basis. Note the use of the word "some". You do not need to completely empty and refill goldfish tanks every week. For one thing, that's not particularly good for the fish. What you want to be doing is removing as much waste as you can with each water change, and taking out and replacing only about a quarter of the water volume each time. One problem that can happen if you change all the water out (besides having to remove the fish in the process), is that significant differences in temperature between the old water and the new water can be extremely stressful to the goldfish. By taking out and replacing only a portion of the water at one time, temperature changes are minimized.
When you do settle upon a tank that is large enough, it is obviously going to be very heavy. Twenty-gallon tanks when filled, will contain 160 pounds of water. Add that to the weight of the empty tank, and you can see the need to have a very sturdy stand or piece of furniture to keep the tank on. The location of the tank is of importance as well. Keep the tank away from heat sources. Goldfish are not tropical fish. And keep the tank out of direct sunlight. Indirect light is best. Do not keep the tank and fish in a darkened room for long, the goldfish will start to lose their characteristic colors! A lighted tank where the light is on no more than 8 to 10 hours a day is about right. Fluorescent lights are often a good choice for hood or canopy lighting.
Goldfish are not simple-minded as some would believe, but are actually somewhat intelligent, and have a sense of curiosity. You can put plenty of things in goldfish tanks that the fish can swim through, around, or under, adding a little variety to their routine. Gravel on the bottom is almost a must, plus the fact that the fish seem to enjoy nosing around in the gravel. Just avoid things which may have sharp edges which could cause injuries to the fish.
While it may seem to be quite a huge enterprise for a few fish, large goldfish tanks are the price that must be paid if you plan on having healthy fish for a number of years.