This is the most popular kind of aquarium, and for beginners, children, the busy or the poor - it is the most practical. Housing Aquarium tanks come in all shapes and sizes from tiny beta bowls to 500 gallon reservoirs. Regardless of the gallon capacity you choose, it is best to select the classic rectangular shape glass tank since the oxygen exchange that occurs between the outside air and the water in the tank is proportional to the air-water interface dictated by the shape of the tank.
Tropical fish thrive in tanks with larger surface areas on top where oxygen levels are greater.
In other words, Wider is Better. If you are using a bowl or hexagon shaped tank, fill it less than 10 inches to the top so that more oxygen exchange can take place. The tank should be covered, with hinged access panels for filters and feeding. You should also provide a light source as some fish will not eat without it. Fluorescent and incandescent types that come with canopy tank hoods are fine.