A large fish can be kept in a small tank but the fish will grow to the size of the tank If the tank is smaller than the maximum size of the fish the fish will grow up deformed with internal organ dysfunctions.Consider buying a tengallon freshwater aquarium The tank itself may cost about 15 dollars US the power filter 20 dollars US the heater if keeping tropical fish 12 dollars US ten pounds of sand gravel 12 dollars.Be sure that your feng shui fish tank is not clamoring for attention with other elements in your room By having it where you also have a fireplace say in a living room the fish tank may not work These two strong large elements may compete for attention and will not result in harmony.