Advice: With the availability of mini-aquarium packages it's become appealing to go small. However, for beginners, choosing a small aquarium is courting failure. Why? Because when the water volume is small, key water parameters change very quickly, leaving no room for error.
Even experienced aquarists are challenged by a small aquarium. Newcomers to the hobby, stay away from tanks under 20 gallons until they've gotten some experience under their belt. Remember, the bigger the tank, the less impact a mistake will have on the fish.