It is a common practice to keep common goldfish in a small bowl, but this allows waste in the water to build up to toxic levels and does not provide enough oxygen. For every small/young goldfish, there should ideally be at least 10 to 20 US gallons (38 to 76 l; 8. 3 to 16. 7 imp gal) of water. A good filter, with no heater, is recommended because these fish can get larger than 12 inches (300 mm). Tank recommendations range up to 75 US gallons (280 l; 62 imp gal). It is possible to keep small goldfish in smaller tanks, but such an arrangement will be very difficult to maintain once the fish grows older. If there is concern about the fish not getting enough oxygen, particularly when it is warm, a water pump, such as a fountain pump, mini pond pump will pull the CO2 water from the bottom, expel it, and the surface action will oxygenate the tank or pond. Contrary to popular belief, air pumps and air stones do not oxygenate directly and rely on bubbles breaking the surface to transfer oxygen to the fish's environment. Ideally, the water pump should push 10x the volume of the tank or pond plus an extra 100lph or gph. Goldfish will die without sufficient dissolved oxygen in the water. A filter that can do at least 10x filtration is best, which means that for every 10 gallons or liters of water, the filter should be able to cycle 100 gallons or liters per hour. If the oxygen in the water runs out then the fish may die or become unconscious. It is advised to move the fish to a basin of water full of fresh water.