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8 Best Fish for a 20-Gallon Tank, & How Many Can You Fit?

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By Lindsey Stanton

a pair of Bolivian ram cichlids in the aquarium

The 20-gallon tank is the most popular fish aquarium among many fish keepers. This is because it offers exciting opportunities and it’s suitable for beginners and hobbyists.

Its small size is ideal for keeping it anywhere, whether in the living room, bedroom, or office, and it’s large enough for keeping a wide variety of fish. Besides, the tank allows you to add some plants, critters, and decorations to ensure the overall health of your aquarium is maintained.

It’s an uphill task to choose the best fish for your 20-gallon tank since it needs you to consider many things. First, you need to know the fish grows up to which size and fully understand the fish’s needs before stocking them. You also need to know how many fish can perfectly fit in a 20-gallon tank.

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The following are the best fish for a 20-gallon tank and how many can fit inside:

The 8 Best Fish for a 20-Gallon Tank

1. Panda Corydoras

panda corydoras
Image Credit: tarzan1104, Shutterstock

These are the smallest and most beautiful Cory catfish species. They grow up to 1.75-2 inches long, and they can fit six or more in a 20-gallon tank.

These little scavengers make great additions to a smaller 20-gallon aquarium. They are peaceful bottom dwellers who like their environment at 72–77°F with plenty of frozen bloodworms and Repashy gel food on hand for any hungry mouths that may arise.

If you keep them well-fed and happy, then soon enough, you will see some breeding behavior going on, and sticky eggs will cover the tank walls.

2. Platy

Southern platyfish
Image Credit: topimages, Shutterstock

The platy, or the platyfish, is one of the most attractive freshwater aquarium fishes. Though small, they are very active and easy to care for and have a peaceful temperament. A 20-gallon aquarium can comfortably accommodate up to eight platies.

Manila-type platies are some of the smallest members of the platy family of fish. They are also one of the most common platies to be kept as aquarium pets. These platies are extremely hardy and can tolerate a broad range of water conditions many other tropical fish cannot.

Normally, platies will only grow to about 2 inches in length. Most platie varieties reach sexual maturity by age one year, and they can live for several years.

3. Rosy Tetra

Rosy tetras are rosy-colored fish with three black vertical bars on their sides. They are hardy fish that adapt well to aquarium life, making them suitable for beginners.

You can keep up to six rosy tetras in a 20-gallon tank. They do better in water conditions of up to 75°F to 82°F.

The rosy tetra attains a maximum length of 2 inches and has an average lifespan of 2 years. They are compatible with many fish of different species, but they tend to chase the rosy tetra while swimming horizontally or at a close distance.

The rosy tetra is a relatively peaceful fish, but it will defend itself when bullied by other rosy tetras or when alarmed. It has the potential to become aggressive at times and will flare its fins at enemy rosy tetras!

4. Chili Rasbora

Chili Rasbora
Image Credit: boban_nz, Shutterstock

The chili rasbora is a species of freshwater fish in the Cyprinidae family. It has a red band around its body with black stripes above that and bright colors on the caudal. The chili rasbora can grow to be about 1.2 inches long and are easy to maintain.

Chili rasboras are very peaceful fish and can be kept in a community aquarium. They live well with other small, non-aggressive, bottom-dwelling tank mates such as danionins, smaller barbs, rasboras, and tetras.

They are happiest when kept in groups of 5 or more individuals and are often sold as a group in the pet trade. You should keep this fish in an aquarium with subdued lighting and soft, acidic water.

However, don’t keep him with larger or more aggressive species. It prefers to live in densely planted tanks with the dark substrate for cover.

Chili rasboras are best kept at temperatures between 68 and 75°F (20 and 24°C). They prefer soft, acidic water, with the pH kept between 6.8 and 7.4. The chili rasbora is somewhat sensitive to nitrate levels, so the average owner should use an aquarium filter that does not produce a large amount of waste.

5. Swordtails

swordtail guppy
Image Credit: neohch, Shutterstock

Swordtails are one of the most popular live-bearing fish and are considered to be among the easiest fish to keep in a community aquarium. They have a sword-like appearance that makes them attractive and provides a great variety of color patterns and types that you can choose from.

Swordtails are very easy to care for. They will thrive in a wide variety of conditions but prefer as much light as possible and live plants to hide from predators or hide behind if startled.

Swordtails are fairly active and are bottom feeders as well. They will eat almost anything you offer them and can be trained to take food from your hand. They can take bread, bloodworms, flakes, pellets, and even live brine shrimp.

Swordtails prefer soft water with a slightly acidic pH level of 6–7 when mature swordtails are usually 3-5 inches long. Swordtails are happy when in a group of at least six swordtails that will breed in almost all aquariums.

6. Goldfish

ryukin goldfish
Image Credit: slowmotiongli, Shutterstock

Goldfish are a type of gold and orange-colored fish from the family Cyprinidae. They have become popular pets in households with a garden pond or aquarium due to their hardy nature, relatively small size, low maintenance requirements, and bright colors.

They are relatively peaceful and prefer living in water conditions 68°F to 74°F. You can keep two goldfish in a 20-gallon tank.

A goldfish’s lifespan can be as long as 20 years if well maintained. The size of goldfish can vary depending on their type and age, but they can grow to be large if given more food to eat. Some goldfish grow up to 6 inches based on species.

7. Leopard Danio

Image Credit: Grigorev Mikhail, Shutterstock

This is a small fish that belongs to the Danionidae family and has an average life expectancy of 2 years. The fish grows up to 1.5 inches long and does better in an aquarium that does not exceed 27 degrees Celsius (80°F)

Leopard Danio has a blackish body with leopard-like spots along its sides with visible fins and red eyes. Leopard Danio feeds on mosquito larvae, brine shrimp, bloodworms, and daphnia.

They are peaceful fish that can be kept in schools of six or more together with other peaceful species such as guppies and mollies. Leopard Danio also attains maturity within three months if proper care is taken. They are ideal for a beginner aquarist.

Leopard Danios need plenty of space to swim about; they thrive best at a temperature of 28-30 degrees Celsius and keep them away from direct sunlight. This fish is a sensitive fish that can easily become ill if water parameters are not maintained correctly.

8. Fancy Guppies

fancy guppy
Image Credit: sufeca, Pixabay

Fancy guppies are one type of guppy, a fish that belongs to the Poecilia genus and Poeciliidae family. They have colorful patterns and fin shapes that make them look so beautiful.

Fancy guppies come in many different colors and patterns, with the red multi-color fancy guppies being the most popular Fancy guppies. They have golden coloring and a black stripe along their spine with red spots around them.

They are very peaceful and freely interact with other species. Fancy guppies are also highly active; hence they need more swimming space. Since they are relatively small in size, you can place 10-12 guppies in a 20-gallon tank.

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Before selecting any fish for your 20-gallon tank, consider the fish’s adult size because most fish stores sell growing fish that are yet to mature. Also, look at the fish behavior and compatibility since some are peaceful while others are aggressive. Besides, some species are not very active, while others are extremely active and need more swimming space.

You also need to be careful with the water parameter because different species have their own preferences. Ensure you choose fish species that can share the same temperature, pH, and water hardness.

The above are the best fish for a 20-gallon tank. Choose one, and you won’t be disappointed.

Featured Image Credit by: DMITRII STARTCEV, Shutterstock

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