It’s a common misconception that a goldfish can live in a tiny bowl. In order for him to survive for any length of time, you’ll need to do frequent water changes and cleanings of bowl – that’s a lot of work and living in a bowl isn’t much fun so it’s best to keep your fish in a regular tank with a proper filtration system.

The size of your tank depends on how many goldfish you want to keep in it. A good rule of thumb is to allocate about 7 gallons of water per fish, so if you want 5 goldfish a 35 gallon tank is recommended. It’s better to keep fish in a long tank that has plenty of surface to air space as goldfish like to have a lot of oxygen in their water. A tall hexagon shaped tank won’t be best tank for these fish.

And here's a list of some:

Firstly, look for physical characteristics of good health. A healthy fish should have bright body color, not pale or dull. However darker or patchy coloration may be an indicator of stress and not of bad health. Before you buy a fish, find out how it should look under normal conditions. No open sores, boils, ulcers, peeling scales or blemishes. No visible parasites, such as tiny white crystals that look like salt or tiny black nodules that look like "blackheads". There are also viruses, like Lymphocystis (cauliflower-like growths on edge of fins). Be sure to examine fish before buying it.

Eyes should be clear, not cloudy or popping out of sockets. Fins are erect, especially top fin (dorsal). Buckled fins can mean trouble. No ragged, torn or ripped fins. All of them should be intact.

Scales are flat and smooth, stomach is well rounded, girth of entire body is of normal size, not bloated or sunken. Visible fish waste should be dark in color, not pale.