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How Many Goldfish in a 20 Gallon Tank?

How Many Goldfish in a 20 Gallon Tank?

A lot of people don't realize that goldfish can grow quite large, and as a result, they overcrowd their tanks. As a result, many goldfish find themselves in the unfortunate situation of being kept in little bowls or aquariums that turn out to be too small for their long-term welfare. In truth, goldfish must stay in a 20-gallon aquarium to be healthy and fulfilling.

In this guide, we will discuss why 20 gallons is usually the minimum tank size for fish, what tank sizes are typically recommended for goldfish, and what factors affect this associated number.

Goldfish Require At Least 20 Gallons

Goldfish are generally thought to be "low-maintenance" aquarium fish that can be kept in a small bowl or aquarium. However, this could not be further from the truth—goldfish are messy, smelly, and require a lot of maintenance and care.

One of the most important things to remember about goldfish is that they'll grow quite large. Depending on the variety of goldfish, they can range from 2 feet to 6 inches. As a result, they need a lot of room to swim around and move about.

Therefore, 20 gallons is the smallest tank you should get for goldfish, but it is essential to keep in mind that the 20-gallon tank size is only the minimum. If you want your goldfish to thrive, consider getting a bigger tank.

How Many Goldfish in a 20 Gallon Tank?

How many goldfish can you hold in a 20-gallon aquarium? We will explore the factors relating to this number later, but you're able to generally keep up to two fish in a 20-gallon tank.

The idea is that you should allow a gallon of water for every inch of fish you have. Common goldfish can grow up to ten inches in length, so two fish is the maximum number of fish you could keep in a twenty-gallon tank.

Of course, this is just an estimate. By overloading the number of fish in your tank, you're putting a lot of stress on the fish and your aquarium. For that reason, it's best that you err on the side of caution and give your active fish a little more room to swim.

What Affects The Number Of Goldfish You Can Keep In A 20 Gallon Tank?

Let's now define the number of goldfish that you can keep in a 20-gallon aquarium.

Goldfish Species

Initially, you should think about what sort of goldfish you have. Although goldfish come in a number of sizes and shapes, you need to consider the type of goldfish that you have.

For example, comet fish can grow up to 12 inches long, while fantail goldfish tops out at about 8 inches. As a result, you would be able to keep 2 fantails in a 20-gallon tank comfortably, but it would not be possible to keep 1 comet.

In principle, you could keep more than two goldfish of smaller varieties in a 20-gallon tank. However, it is important to bear in mind that goldfish are active fish and need a lot of space to swim, so we would recommend sticking to two fish as the maximum number of a 20-gallon tank.

Frequency Of Tank Maintenance

Your fish's health depends on the cleanliness of their tank. By performing regular water changes and vacuuming the gravel, you help maintain the tank's cleanliness, which in turn boosts the overall health of your fish.

The volume of tank maintenance can determine the number of goldfish you can keep in a 20-gallon tank. Although goldfish can be rather hardy fish, they're nonetheless sensitive to the environment. A dirty aquarium can cause various illnesses for your goldfish, such as diseases or infections.

Fish owners have a responsibility to ensure that their aquariums are clean and safe. Paying attention to more regular water changes and cleanings should enable you to keep your fish in your 20-gallon tank.

Tank Layout

Another factor that can affect the number of goldfish you can keep in a 20-gallon tank is the layout of your aquarium. There are two kinds of goldfish tanks: planted tanks and unplanted tanks.

Planted tanks often have more plant life and decoration, making it easier for your fish to hide and seek out prey. These tanks are more attractive, but they can also reduce the amount of available space in your aquarium.

On the other hand, unplanted tanks have a simpler design. This will help your fish have a more extensive swimming area, giving them a feeling of empowerment and placing them under tension.

The setup of your fish pond can affect the number of fish you can preserve. If you have a planted tank, you might prefer to keep this with only 1 fish. You can also maintain 2 or 3 fish in an untapped tank.

Special Considerations For Small Tanks

Small tanks, like 20-gallon tanks, have their own range of challenges. In addition to the principles and rules that apply to larger tanks, you ought to observe a few other things if you were to restock a small tank.

Watch Out For Aggression

Because goldfish are not aggressive fish by nature, they can become aggressive if they feel stressed or territorial. This is so more likely to be the case in a small aquarium where your fish do not have enough space to swim and explore. The lack of enough space may cause your fish to attack each other, causing injuries.

Make sure to provide your fish with lots of room to swim. In a 20-gallon tank, we recommend having a single goldfish or at most, two small goldfish. If they re still juvenile, you may choose to keep between 1 and 4 fancy goldfish, but it s ideal to be careful and have them all stay apart.

Test Water Parameters Frequently

Bear in mind that because your tank has less water in it and supplies are less immediate, waste and debris can accumulate more quickly. Regardless of whether you re a small or large hobbyist, it s a good idea to check your water parameters regularly to ward off potential problems with goldfish.

Do not to have a crowded fish pond by abiding by the rule of having 1-2 goldfish for each 20 gallons in the fish pond. Then, you can begin employing a more creative plan to keep your pond clean. For instance, when looking for protein-based fish food, choose foods with less filler and more natural ingredients.

Healthy foods can reduce the garbage in your tank.

Careful vacuuming of your gravel with a gravel vacuum can help remove debris and waste from the water, improving your water quality.

We recommend using a filter that's twice the size of your 20-gallon tank. As your filter gets bigger, it will help keep your water clean and reduce stress on the fish in your tank.

Growth May Be Stunted

Across all aquatic species, the typical evolution of a common adult fish body matches its home aquarium size well. As such, adult goldfish, which grow quite large, will generally not develop into the full adult size allowed by a standard aquarium.

Though this doesn't mean that your fish will be unhealthy, it's something to keep in mind if you re considering keeping goldfish in a 20-gallon tank. Hobbyists looking to maximize goldfish growth often opt for larger tanks, such as 30-gallon or 40-gallon tanks.

In addition to keeping an aquarium that is the right size for your fish's needs, you don't need to be concerned! There are many steps you can take to make sure that their lives are excellent. By sustaining a close watch on your water parameters and following the instructions below, you'll be able to give your pet the best care available.

Therefore, for a period of five to 10 years, you'll have ample time to enjoy your goldfish.


To sum it up, we recommend keeping a single goldfish or two in a small 20-gallon tank. If you happen to be thinking about keeping fancy goldfish, you can keep 1-4 together as long as they are still juveniles. Just remember, it is best practice to err on the side of caution and keep them separate.

While keeping your fish healthy, remember that small tanks can experience water-quality issues more quickly than larger tanks. Consider testing the water parameters on a regular basis and utilizing a filter made for a tank that's twice the size of your 20-gallon tank.

We hope this article was beneficial! Remember, if you have any questions about goldfish maintenance, our team of experts will always be here to assist. And to learn more about the care needs of goldfish, review our other articles. Happy goldfish care!

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