The best goldfish tank for you depends on how many fish you plan on keeping as pets. The more fish you own, the larger the aquarium you will need. Look at both the shape of the tank and the amount of water it can hold when picking it out. Although a goldfish kept in a bowl is a common image, you want to avoid choosing a small, bowl-shaped aquarium, as it is too small, even for a single fish. Bowls also do not allow you to put a filter in the water, which fish need to survive.
The average recommendation for the size of a goldfish tank is at least 10 gallons (38 liters) per fish. Some people recommend getting at least a 20-gallon (76-liter) goldfish tank for a single fish and adding 10 gallons (38 liters) for each additional fish. Still others suggest getting a 40-gallon (152-liter) tank even for a single fish. If you own three goldfish, your tank should be no smaller than 30 gallons (114 liters). While it's possible to get a tank that is too small, it's very difficult to get a goldfish tank that is too large.
Surface area of the goldfish tank is another important consideration. To find the surface area of the aquarium, multiply its length by its width. Each fish in an aquarium needs about 30 square inches (194 square cm). Determine if the tank is large enough for your fish by dividing the area in inches by 30 or the area in centimeters by 194. The more surface area a tank has, the more air is able to circulate and reach the fish in the water, which encourages growth and good health.
As a goldfish bowl is smaller at the top than in the middle, it is typically not large enough to allow your fish to thrive. Fish release ammonia, which needs to be filtered out of the water so that they do not suffocate. A fish tank also needs to be large enough to accommodate a filter.
The filter is a key part of the tank, because fish produce a lot of waste and bacteria. If the water isn't cleaned out, the fish will die or become very ill. Choose a tank with a built-in filter for ease or choose one that allows you to clip a filter to the side. Ideally, the filter will have replaceable pads.