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Starting out with a pet goldfish is easy. Just place the small fish in a clear glass bowl, feed it, and watch it grow. However, eventually every goldfish owner runs into the same dilemma: What’s the right size of tank for my growing goldfish?
It depends on the specific type of goldfish, but generally the minimum is 20 gallons of water for a single goldfish. Then, add another 10 gallons for each additional fish in the same tank.
It is important to note that there are many types of goldfish, from the most common to fancy. The common variety tends to grow larger than their fancy goldfish counterparts, and therefore have a bigger need for larger tanks.
All in all, it’s clear that a simple small glass bowl should be only a temporary home for a young goldfish. Not long after that these active swimmers need the space to move about.
Minimum Tank Size for Goldfish Types
Fancy goldfish ~ e.g. those with double tails ~ usually grow to about 8 inches long, but some could reach up to a foot long. Many owners point to a tank of at least 50 gallons for them. Even more for more than one fancy goldfish ~ this type of goldfish is known to become territorial thus it’s a good idea to allow adequate spacing between them.
Single-tailed goldfish can grow even larger! Mature adult common goldfish can reach up to 18 inches in length, at which point the aquarium needs to be 75 gallons, or 150 gallons for more than one.
When a Goldfish Tank is Too Small
Goldfish in too-small tanks can have their growth hindered because they didn’t have enough space to swim around and explore, as goldfish are apt to do. Goldfish are active fish and need the ability to move around constantly to stay in top shape, or to avoid conflict with other fish.
This would limit the growth of your goldfish at a ripe adult age, and also threaten to make that lifespan even shorter. It’s important for your fish to have an adequately sized environment. Unhappy goldfish are more apt to suffer from health issues, and besides, unhappy fish can be no fun to watch!
About That Minimum Size Tank for Goldfish
We want to revisit the minimum size of tank for your goldfish, because if you do even a little bit of research online, you will most likely get a range of answers. Part of this is because some goldfish owners or breeders are total fanatics, and tend to overstate or exaggerate the needed size of an aquarium.
But mainly this is because it totally depends on the breed of goldfish. Some grow faster than others; while even others hardly grow at all. Some look long but only have really extended tails; others can grow more up and down rather than longways.
For instance, one owner of the fancy goldfish breeds celestial or telescope says they can be held for life in a tank of about 30 gallons for one, plus 10 more for each additional fish.
We stick with what we stated at the start, that is, generally allow at least 20 gallons for the first goldfish, then 10 more gallons for each fish added. Remember, this is a starting point, so you wouldn’t have to stick with just 20 gallons for an extended period.
Some enthusiasts call it a general rule of thumb to have 5 gallons for every inch of goldfish, regardless of the breed. With this, of course, you would have to eyeball the size, since it’s difficult to hold a ruler up to a goldfish to get a measurement.
About Those Fancy Goldfish
Human beings sure have created a lot of different breeds in many fish and animals, and the goldfish is no exception. Apparently someone long ago decided that the simple, common goldfish was not enough, so they began tinkering with mating different types together to create new goldfish species altogether.
Fancy goldfish have been selectively bred with purposes like new colors or styles of tails or fins. A drawback is that, due to this selective breeding, fancy goldfish can tend to be a bit more rambunctious, or at times stubborn, and they are known to be less hardy than their common counterparts.
Common goldfish are better at tolerating the surroundings given to them. Fancy goldfish can be rather spoiled, and command larger tanks. In other words, fancy goldfish can tend to have unique personalities, perhaps something goldfish owners desire.
It can be important to know which type of goldfish you have. If they look pretty plain in a gold or somewhat orange color with single tails, they’re most likely common goldfish. In the United States, the comet goldfish is quite common.
But it is estimated that there are over 100 different varieties of goldfish. Many have super unique colors or color patterns, and physical details like double tails, or very elongated tails that flow behind them like an elaborate wedding dress!
While the gold or bright orange types can be considered common, in the wild it is actually more common for goldfish to be kind of a gray-silver in color, or even gray with a touch of olive green.
Different Types of Goldfish
As noted above, the size of the tank depends on the type of goldfish, and also their age because indeed, goldfish do grow in size. Here is a brief list of goldfish kept as pets worldwide, with details on how big they might grow, to help give an idea about tank size needs.
Fancy Goldfish
These specially bred goldfish can reach up to a foot long ~ and even up to a foot tall including tail and fins! Some grow outward too, maybe even as large as a small grapefruit.
- A red oranda once grew to 14 inches long
- Fantail varieties also can get up to 14 inches in length
- Ryukin goldfish are a variety of the fantail family, and can have tails twice as long as the body! This means they need larger aquariums for the ability to turn around.
Common Goldfish
- Common goldfish can grow up to 14 inches long
- The longest common goldfish to date was caught at 20 inches!
Water Quality in Goldfish Tanks
The size of a tank or aquarium is not the only health-related concern for new goldfish owners. Goldfish are a species in the carp family, and as such produce a lot of waste, both from their feces and through the gills.
They basically, naturally, release harmful chemicals so the water should be watched carefully. Too much build-up of this waste could reach toxic levels, and in a relatively short amount of time. Sometimes the result is the death of a goldfish, which is unfortunate and can be avoided.
Again, each goldfish should be in about 20 gallons, and then add 10 more gallons per fish added. Goldfish (which are smaller) should have about 10 US gallons (38 L; 8.3 imp gal) per goldfish.
When they exhale through the gills, there is a process of the oxygen diffusing, a reason why it’s wise to have an active aeration via a water pump, filter, or fountain. The idea is to agitate the surface, to basically mix it up so it doesn’t become toxically still.
Goldfish are coldwater fish, and the optimum temperature of water should be 68 to 72 degrees Fahrenheit (20 to 22 degrees Celsius).
It is important to note that when changing the water of a goldfish tank, to leave about 40% of the old water in there. That is, replace only about 60%. This is to not shock a fish by the new environment.
Related Questions
Question: Why do goldfish grow less in tanks that are too small?
Answer: We think it’s because they are unhappy, but some point to studies that indicate fish can produce a growth-inhibiting hormone, so when space around them is tight, the hormone accumulates and hinders growth.
Question: Who counts all the breeds of goldfish?
Answer: Scientists and ichthyologists ~ those who study everything about fish biology including anatomy, behavior, their environments, and how they socially interact with one another and with other fish. While many acknowledge that there are over 100 goldfish types, some say that may greatly underestimate. Some reports are that there are over 200 goldfish breeds alone in China ~ which is where most goldfish breeding occurred.
Question: Can you pet a goldfish?
Answer: Like almost every type of fish, goldfish do not like to be petted. In fact, it could be harmful to a protective layer around its exterior, and is not recommended.
Question: Can goldfish change colors while you care for them?
Answer: It’s possible. A goldfish’s color is determined by diet, and exposure to light, as well as age and health. Goldfish left in the dark over extended periods are known to change to an almost gray color.