how large does goldfish get?
Get a large enough tank. The minimum tank size for one goldfish is 10-15 US gallons (56.7 liters)(Remember, they grow to about 10-12 inches (25.5-30.5 centimeters), and sometimes over!) and you will need to add 10 U.S. gallons (37.8 liters) onto that for each additional goldfish.