15 Best Fish for a 20-gallon Tank

Best Fish for a 20-gallon Tank

15 Best Fish for a 20-gallon Tank7 mins read

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Best Fish for a 20-gallon Tank
Image from Flickr

There are so many incredible fish species available, and choosing the best fish for 20 gallon tank environments can be overwhelming. Often, in the pet shop, there is so much choice that it can be hard to choose a few favorites. Luckily if you have a 20-gallon or larger tank you could easily keep a few species together in a community tank.

A community tank essentially is a well-established tank with fish of different species. However, the best fish for a 20 gallon tank need to have similar water parameter requirements. Also, they need to get along with each other.

Thus choosing the 15 best fish for a 20-gallon tank is not as easy as it seems. You need to carefully consider each species, and how they will interact with each other. This article will also cover topics like how many fish in a 20 gallon tank, as well as how many fish can be in a 20 gallon tank for breeding purposes.

Table of Contents

How Many Fish Can Be in a 20-gallon Tank?

Are you wondering how many fish can be in a 20 gallon tank? A 20-gallon tank is the perfect sized tank for a community set-up or beginners.

You can easily create a majestic and appealing display with a 20-gallon tank. To answer the question “how many fish can be in a 20-gallon tank” It all depends on the fish species and their individual space needs.

The size is perfect to keep a community of fish species, and many plant species.

Even for experts who want to expand their horizons with a few more exotic fish species in a community tank. A community tank creates an excellent opportunity for playing around with a few fish species or varieties. However, choosing the best fish for 20 gallon tank setups is not always easy.

With a 20-gallon tank, you could easily opt for medium to slightly larger fish if you are keeping a small similar group. On the other hand, you can go the other route with smaller fish species. Keep in mind never to overcrowd this size tank. Thus, the set-up and fish species that you want to keep must be carefully planned.

With that note, it is vital to understand which fish species will thrive together in a community tank, as well as their basic care needs.

Why Choose a 20-gallon Tank

Image from Flickr

If you are wondering how many fish can be in a 20 gallon tank you may be tempted to get a larger tnk so you can get more fish. But first here are a few benefits of choosing a 20-gallon tank:

  • Because it is a smaller-sized tank it is more readily available and affordable.
  • Similarly, you will need less, and less expensive tank equipment. Very large tanks often need much more expensive, or double the equipment.
  • The tank will not take up too much space in your home. A 20-gallon tank is usually around 2 – 2.5 feet in length and is ideal for smaller spaces.
  • The tank even filled with water will still be quite lightweight. It will be sturdy and lightweight enough for most stands or furniture pieces.
  • Though small, it is still big enough to maintain healthy water conditions and good quality stability in parameters.
  • On the other hand, the tank is also small enough for regular water changes and cleaning.
  • The size is perfect to house either a few medium to larger-sized fish or smaller medium-sized fish.
  • You can easily set up a gorgeous community tank with plenty of fish species and plants.

Best Fish for a 20-gallon Tank

Before jumping into all the exciting fish species that you could house in your tank, you must understand their grouping.

With any tank set-up, there is usually a more acceptable guideline to follow in grouping them. Grouping means introducing species that have similar requirements, but different functions or personalities. However, keep in mind, that this is not a must, but rather just a rule of thumb.

Fish species in an aquarium are typically categorized into these three groups:

1. Center Piece Fish

A centerpiece fish is habitually your main attraction. Mostly they are larger fish that stand out from the crowd to make a statement. Regarding the best fish for 20 gallon tank setups, you may only need one or two. Centerpiece fish are mostly species that are not kept in groups, but rather a pairs, or single. You can usually keep centerpiece fish in groups of 3 at most. Essentially, it is highly advised only to have one centerpiece fish species. This is because they are often larger, predatory, or more territorial fish species. Center Piece fish are usually species that remain in the mid or top sections of the aquarium.

2. Schooling Fish

Now, schooling fish will be what makes up the bulk of your tank. If you are wondering how many fish in a 20 gallon tank is best, remember different species need different school sizes.

However, they are usually fish species best kept in groups of six or more fish. Ideally, you could keep a few different groups of schooling species together. Regarding that, they are suitable tank mates. A group of schooling fish such as the brightly colored tetras, have a certain charm, swimming around a communal aquarium.

They are what bring life to your aquarium, and usually provide a bit more activity in the tank. For the best fish for 20 gallon tank setups, guppies and danios are two popular examples. Schooling fish typically utilize the top and mid sections of the aquarium.

3. Bottom Feeding Fish

No aquarium is complete with one or more bottom-feeding fish species. They add a layer of fun and interest to the bottom area of your tank. Plus, they are also usually scavengers or algae eaters. Most bottom feeders will clean up all the wasted food particles from your other fish groups. Bottom-feeder fish species are mostly peaceful and usually get along with plenty of species of tank mates. There are so many species to choose from. They often fall into the categories of loaches, catfish, plecos, and many more. However just keep in mind, that many bottom-feeding species grow quite large. Thus, enquire about their sizes first before adding them to your aquarium. For the best fish for 20 gallon tank setups, small fish like panda loaches are ideal.

With that covered, here are a few species from every group that are quite popular in community tanks. Remember that you do not have to stick to the exact three groups. You can mix and match as you please, or stick to a single species.

What Are the 15 Best Fish Species for a 20-Gallon Tank

Center Piece Fish

1. Betta Splendens (Siamese Fighter Fish)

Betta Splendens
Betta fish are omnivores and require a well-balanced diet. Image from Flickr

The Betta fish is by far the most popular Centerpiece fish in the aquarium trade. Besides the Goldfish, which is a whole other scenario. Betta fish were originally domesticated in Taiwan as fighter fish, used for gambling. This is because males show extreme aggression towards each other. Keeping two males together will ultimately result in them fighting to death. Females are less aggressive, though they tend to form a hierarchy. That is why it is critical to have at least 3 females or more. Two females will ultimately squabble. The one will completely dominate, even to the point of killing the other.

You may have seen plenty of Betta fish in pet stores, with their vibrant colors, and long flowing fins. Often, they people keep them in bowls, which is just downright cruel. Bettas like any other tropical fish need a sizeable tank, water filter, and heater. A single Betta can easily live in a 5-gallon tank, though 10 gallons is more adequate. Betta fish hardly ever grow larger than 3 inches (7.6 cm), unless they are the Giant breed.

  • Description:

Betta fish come in a vast range of colors, solid color, Bi and tri colors, and even marbled colors. Similarly, they also have many different fin and tail variations. The Plakat is the most common species of Betta. It is the closest relative to wild Bettas. Plakats have short fins and a short-rounded tail. Other tail variations such as Veiltail, Rosetail, Halfmoon, Delta, and Crown tails are also quite popular. The most popular colors are usually red or blue. Though they are available in almost every color you could imagine.

  • Origin and Natural Habitat:

Betta fish originate from Thailand. However, they are available all over the world today. Their natural habitat consists of shallow moving water, such as marshes, streams, and ponds.

  • Temperament and Behaviour:

Betta fish are highly aggressive. Males will most certainly kill each other. Though a few females will get along together. Suitable tank mates are usually fast-moving schooling fish, that do not have long-flowing fins. Bettas have an innate desire to nip at fish that “look better than them”.  Usually, peaceful bottom-feeding fish are usually left alone by Bettas. If you are asking how many fish in a 20 gallon tank is best, remember that male bettas cannot be kept with others of their own gender.

  • Tank and Water Requirements:

Bettas require clean water with a filter that has a moderate to soft current. They thrive in temperatures around 70 – 80 ̊ F (21 – 27 ̊ C), and a pH level of between 6.5 and 7.5.

  • What to Feed:

Betta fish are omnivores and require a well-balanced diet. They need quality flakes or small pellets as a staple. Additionally, proteins such as brine shrimp, bloodworms, and daphnia can be fed. You can also give small amounts of blanched vegetables such as zucchini, lettuce, shelled peas, and spinach.

2. Honey Gourami (Trichogaster chuna)

Honey Gourami
The Honey Gourami is a yellowish color, usually with red markings at the base of the tail and fins. Image from Flickr

The Honey Gourami is an easy-going and peaceful centerpiece fish. It is an attractive fish, and one of the best fish for 20 gallon tank setups if you want something less common. You should ideally keep them in a in a male and female pair or as a single fish. The Honey Gourami is smaller and less noisy than the dwarf gourami. Thus, a better choice for communal tanks. The Honey Gourami averages around 2.5 Inches (5.5 cm) in size.

  • Description:

The Honey Gourami is a yellowish color, usually with red markings at the base of the tail and fins. It has black coloring on the underside of the body and fins. Though a few variations occur. More colors are the lighter solid yellow or orange-yellow variations.

  • Origin and Natural Habitat:

They are native to India. Their natural habitat consists of lush vegetated rivers and lakes, with low mineral waters. They are top and middle-dwelling fish in the aquarium.

  • Temperament and Behaviour:

Honey Gourami’s are quite peaceful and ideal for beginners. They usually get along well with schooling fish and bottom-dwelling fish. They may become slightly territorial during spawning though.

  • Tank and Water Requirements:

These fish require clear water conditions with a slow current. Ideal temperatures are between 72 – 81 ̊ F (22 – 27 ̊ C), and a water pH of between 6.0 – 7.5.

  • What to Feed:

Gouramis are carnivores and will flourish on high-quality food for their species. Specialized pellets or flakes that you purchase from a pet store. Other than that, you should supplement their diet with proteins. these include brine shrimp, blood worms, shrimp pellets, daphnia, and spirulina.

3. Dwarf Cichlid (Apistogramma)

Apistogramma
The dwarf Cichlid originates from the more tropical South America. Image from Flickr

The Dwarf Cichlid is the perfect size and centerpiece addition to your aquarium. A dwarf cichlid requires at least a 10-gallon tank; thus a 20-gallon is more than enough. It is vital only to keep a single dwarf cichlid in your aquarium, or a male and female, with other species.

  • Description:

One of the most colorful species, the Dwarf Cichlid typically has an orange body tone, with blue gills, and red and blue-tipped fins. The eyes have red around them, and there is iridescent blue on the scales of the body. However, Dwarf Cichlids are available in quite a few color variations. Some include the Cockatoo Dwarf or Red Fin Dwarf cichlid. Dwarf cichlids are usually around 2-3 inches (5 – 8 cm) in size.

  • Origin and Natural Habitat:

The dwarf Cichlid originates from the more tropical South America. They inhabit slow-moving streams and quiet backwaters. Often also other still-water areas with sandy substrate and rocks. This makes them one of the best fish for 20 gallon tank setups that have slow moving water with a sponge filter.

  • Temperament and Behaviour:

Dwarf Cichlids, like most cichlids, are territorial and slightly aggressive. Thus, be carefull when picking tank mates. They are bottom and mid-level dwelling fish. They get along well with most bottom dwellers and schooling fish that are fast-moving.

  • Tank and Water Requirements:

They require clear water with a slow current. Brackish water is a preference with a neutral pH of around 6.0 – 7.0. Try to maintain temperatures between 74 – 80 ̊ F (23 – 27 ̊ C).

  • What to Feed:

Because they are omnivores, they require a more varied diet. Good quality cichlid pellets or flakes make up their staple food. You can enrich their diet with blanched green vegetables, proteins, such as brine shrimp, and blood worms, and spirulina.

4. Kribensis (Pelvicachromis pulcher)

Kribensis
Kribensis have a colorful display of reds, silvers, black, and purple on their bodies. Image from Flickr

Another gorgeous centerpiece fish is the Kribensis, one of the most colorful of all the best fish for a 20 gallon tank. It is ideal for beginners and community aquariums. The Kribensis has eye-catching colors with contrasting stripes, giving it a colorful appeal. It usually reaches between 3-4 inches (7.6 – 8 cm) in size.

  • Description:

Kribensis have a colorful display of reds, silvers, black, and purple on their bodies. They are similarly available in a few color variations.

  • Origin and Natural Habitat:

They naturally occur in West Africa, as part of the cichlid family. They enjoy slow-moving sandy rivers and streams with slightly acidic to neutral parameters.

  • Temperament and Behaviour:

They are African cichlids, however less aggressive than most cichlid species. They are usually more territorial during spawning, and will easily breed in your aquarium. Because they are bottom and mid-dwelling fish, top-dweller tank mates are more suitable. Other schooling species and most peaceful bottom feeders should suffice as tank mates. Overall, they are one of the best fish for 20 gallon tank setups if you want a beginner cichlid or are new to cichlids.

  • Tank and Water Requirements:

Their ideal temperature is between 75 – 81 ̊ F (24 – 27 ̊ C), and a pH of 5 – 7.5. If you are wonderinghow many fish in a 20 gallon tank can be kept easily, remember the more fish, the more often you will have to clean.

  • What to Feed:

Kribesnis are omnivores, essentailly. They require a diet with high-quality pellets, supplemented with proteins and vegetables. Proteins such as brine shrimp, bloodworms daphnia, and mosquito larvae are ideal. Blanched green vegetables such as zucchini and spinach are similarly good options.

5. Bolivian Ram (Mikrogeophagus altispinosus)

Bolivian Ram
Bolivian Rams usually range in size between 2.5 – 3 inches (7 – 7.6 cm). Image from Flickr

The Bolivian Ram fish is an eye-catching centerpiece fish. The species is more suitable for experienced aquarists and has more specific needs. However, it is one of the best fish for a 20 gallon tank if you’re looking for cichlids. Essentially Bolivian Rams need a mate, thus it is best to keep a male and female together in a communal tank.

  • Description:

Bolivian Rams usually range in size between 2.5 – 3 inches (7 – 7.6 cm). They have a grey and yellow body with a horizontal black stripe. There is a black dot on the side, and the fins have red, blue, and white markings. Other variations such as the Blue, Electric Blue Ram, and Gold Ram also exist.

  • Origin and Natural Habitat:

Bolivian Rams are native to Brazil and Bolivia. Here they inhabit shallow water with dense vegetation and open spaces for swimming.

  • Temperament and Behaviour:

Though territorial when spawning, they are quite peaceful generally. They are mid and bottom-dwelling fish, and easily kept in pairs. Bolivian rams should get along well with most peaceful schooling fish species.

  • Tank and Water Requirements:

In the aquarium, they prefer warmer temperatures of around 75 – 82 ̊ F (24 – 28 ̊ C). A pH of 6.0 to 7.5 is acceptable. Generally, they enjoy arrangements like their natural habitat. This includes sandy substrate, plenty of plants, and open spaces for swimming.

  • What to Feed:

They are omnivores and need a good variation of blanched vegetables, and proteins such as brine shrimp, and bloodworms. A sinkable flake or pellet food is essential as their main meal.

6. Dwarf Gourami (Trichogaster lalius)

Dwarf Gourami
Gourami’s require water temperatures of between 72 – 82 ̊ F (22 – 28 ̊ C), and a pH of 6.0 to 7.5. Image from Flickr

The dwarf Gourami is a versatile and social centerpiece fish for your aquarium. Like the kribensis, it is one of the best fish for a 20 gallon tank if color is what you are after. Because it is a smaller size, around 2.5 – 3.5 inches (6.3 – 8.8 cm), it is ideal for a 20-gallon tank.

  • Description:

Dwarf Gourami is available in a few colors. Their main variations are Powder Blue, Red, and blue-toned colors.

  • Origin and Natural Habitat:

These top and middle-dwelling fish, originate from Pakistan, India, and Bangladesh. They inhabit slow-moving rivers and streams.

  • Temperament and Behaviour:

They are naturally quite peaceful and easy to care for. Ideal for beginners, and quite hardy. Keep them in pairs or groups with a single male, and one or more females. Dwarf Gourami’s usually inhabit the top and middle layers of the aquarium.

  • Tank and Water Requirements:

Gourami’s require water temperatures of between 72 – 82 ̊ F (22 – 28 ̊ C), and a pH of 6.0 to 7.5. You can recreate a more natural setting for them with sandy substrate, rocks, and some plants.

  • What to Feed:

Naturally, omnivores need a vegetable and protein-based diet. Good quality Gourami pellets or flakes are ideal as a staple. Blanched vegetables and proteins such as brine shrimp and blood worms are ideal to supplement their diet.

Schooling Fish

7. Guppies (Poecilia reticulata)

Guppies (Poecilia reticulata)
Guppies are native to South America and found in many water bodies.

With no introduction needed, guppies and Fancy guppies are also some of the most popular and readily available aquarium fish. Their smaller size, brilliant colors, and schooling nature make them ideal for a 20-gallon tank. Guppy males are lighter in color with long flowing tails. While females have shorter tails and less coloration. They are usually around 1.5 inches to 2.5 (3.8 – 6.3cm) inches in size, depending on the type, and gender of the Guppy. Overall, they are one of the best fish for 20 gallon tank setups for beginners due to their hardiness.

  • Description:

Guppies are hardy and active little fish. They are available in fancy or regular variants. There are so many different colors available, some with solid single colors, or multiple colors. There are even varieties with different tail shapes, such as Delta, Sword, Lyre, and many more.

  • Origin and Natural Habitat:

Guppies are native to South America and found in many water bodies. They are tolerant of brackish water up to the point where it almost becomes saline. They are extremely hardy and will survive most water parameters.

  • Temperament and Behaviour:

Guppies are peaceful schooling fish that you can keep with a variety of tank mate species. Advisable however is to keep a ratio of one male per three females. Guppy males do get territorial during spawning. Also, keep in mind Guppies are avid breeders and live-bearing fish. Soon you may have a whole colony in your tank. If you are worried about how many fish in a 20 gallon tank is best, ensure you remove eggs so your tank doesn’t get overcrowded.

  • Tank and Water Requirements:

Luckily guppies are quite tolerant to a range of water conditions. However, temperatures of between 63 – 82 ̊ F (17.2 – 28 ̊ C), and a pH of between 7.0 – 8.5 is more suitable. They are schooling fish and utilize all areas of the tank. You will need a few hiding spots, and some open swimming space to keep them happy in their tank. One guppy can easily thrive in a 5-gallon tank, thus 20 gallons could house a few.

  • What to Feed:

Guppies could easily survive on quality flakes or small pellets. However, to keep them healthy also introduce some vegetables and proteins. Guppies are omnivores and need food in small portions for their tiny mouths. Shred some blanched vegetables for them, and add brine shrimp or bloodworms for protein.

8. Zebra Danios (Danio rerio)

Zebra Danios
Zebra Danios are peaceful, keeping to themselves, and very active.

Depending on your preference, Zebra Danios could serve as a group of centerpiece fish, or schooling background fish. They are an extremely hardy species, ideal for beginners. Zebra Danios have a striking appeal that will stand out in your aquarium. Similarly, their small size of 1.5 to 2 inches (3.8 to 6 cm), makes them ideal for a 10 to 20-gallon aquarium.

  • Description:

The Zebra danio has a greyish base color and dorsal fin. There are yellow and blue horizontal stripes on the body and fins. The dorsal fin has yellow edges. Some variations even pose red coloration and darker grey-blue stripes.

  • Origin and Natural Habitat:

Naturally from India, they are top and middle-dwelling fish. Because they are extremely active fish they will need ample open spaces for swimming, and a few hiding spots.

  • Temperament and Behaviour:

Zebra Danios are peaceful, keeping to themselves, and very active. You will find that they get along well with most other fish species.

  • Tank and Water Requirements:

Zebra Danios prefer temperatures of around 72 – 86 ̊ F (26 – 30 ̊ C), though they can tolerate much cooler temperatures. Water pH is ideal at between 6.5 – 7.8.

  • What to Feed:

Zebra Danio are omnivores. In nature, they eat Zooplankton, Phytoplankton insects, and insect larvae. They also love bloodworms and small crustaceans. You can feed them a quality flake or pellet food, and enrich it with some vegetables and proteins.

9. Ember Tetras (Hyphessobrycon amandae)

Ember Tetras
Ember tetras are peaceful schooling fish, with very few behavioral issues. Image from Flickr

The Ember Tetra is a bold-colored and prominent fish. It does very well in crowded community tanks and requires very little space. Ember tetras usually thrive in small tanks such as 5 gallons or more. They are ideal for beginners and very easy to keep. If you want a peaceful and placid companion, these are easily one of the best fish for a 20 gallon tank to prevent fighting. Ember Tetras are very small around only 0.75 inches (2cm).

  • Description:

The Ember tetra is usually a solid almost translucent red to dark orange color. It almost resembles an actual hot ember.

  • Origin and Natural Habitat:

They naturally occur in Brazill in tropical river basins.

  • Temperament and Behaviour:

Ember tetras are peaceful schooling fish, with very few behavioral issues. However, because of their small size, they could easily become prey to larger predatory fish. Therefore if you are asking how many fish can be in a 20 gallon tank successfully, bear their species in mind. These guys do not mix with other tetras much, either.

  • Tank and Water Requirements:

Ember Tetras thrive in water temperatures of between 72 – 82 ̊ F (26 – 28 ̊ C). They are also quite adaptable with pH levels and can thrive in a slightly acid-to-neutral pH range of 5.0 – 7.0. These fish love densely vegetated areas; thus, a crowded well well-planted aquarium is ideal. They also spend most of their time in mid-water.

  • What to Feed:

Ember Tetra are omnivores and live off plants and small prey. They are usually worms, zooplankton, and tiny invertebrates. It is ideal to feed them a balanced diet with  Nano pellets or crushed flakes, baby brine shrimp, daphnia, cyclops, and rotifers. In terms of tetras, they are one of the best fish for 20 gallon tank environments due to their peaceful nature.

10. Cardinal Tetras (Paracheirodon axelrodi)

Cardinal Tetras
Cardinal tetras require clean water with a moderate current filter. They enjoy temperatures between 74 – 84 ̊ F (23 – 29 ̊ C) and more acidic parameters with a pH of 4.5 – 6.5.

Cardinal Tetras, not to be confused with neon Tetras are colorful schooling fish, perfect for a 20-gallon tank. They may look like Neon tetras, though there are some small differences.

  • Description:

Cardinal tetras have a translucent grey back and dorsal fin. Following is a horizontal metallic blue line, and then a bright red line in the middle. The belly of the fish is a pinkish-white color, and the fins are translucent with a light blue tip. The Neno tetra is almost similar; however, the red line does not run straight through. Neon tetras do not exhibit as much of the blue and red as cardinal tetras. Cardinal Tetras are tiny 1.5-inch (4cm) fish.

  • Origin and Natural Habitat:

They are native to South America where they inhabit the clear Orinoco and Negro rivers. They prefer to stay in the midwater and enjoy slow-moving currents.

  • Temperament and Behaviour:

Cardinal tetras are peaceful schooling fish. They are more suitable for aquarists with a bit of knowledge. They usually get along with the most suitable tank mates. However, they could easily become prey for larger, more aggressive fish species.

  • Tank and Water Requirements:

Cardinal tetras require clean water with a moderate current filter. They enjoy temperatures between 74 – 84 ̊ F (23 – 29 ̊ C) and more acidic parameters with a pH of 4.5 – 6.5.

  • What to Feed:

Tetras are mostly omnivores and the species group overall makes some of the easiest and best fish for a 20 gallon tank. However, it helps to know what to feed. They need a staple diet of micro pellets or small crushed flakes. It is advised to supplement their diet with vegetables such as shelled peas, spinach, zucchini, or lettuce. Proteins such as baby brine shrimp, microworms, daphnia, and small insect larvae are also suitable.

11. Harlequin Rasbora (Trigonostigma heteromorpha)

Harlequin Rasbora
Rasboras require water temperatures of around 70 – 82 F (21 – 27.7 ̊ C) and a pH of 5.0 to 7.7. Image from Flickr

Harlequin Rasbora are very peaceful, and mellow creatures that are ideal for a 10 to 20-gallon tank. They are schooling fish and very easy to keep, especially for beginners. These fish average around 2.5 inches (6.3cm) in size and prefer to stay in groups of around 6 fish.

  • Description:

They have a golden yellow to silvery grey body color, with a black marking on the base. The fins are a silvery translucent color with reddish tips.

  • Origin and Natural Habitat:

They naturally occur in Southeast Asia. They occur in peat swamps, and forest pools with plenty of decomposing plant matter. Thus, they prefer more acidic black water, with plenty of tannins.

  • Temperament and Behaviour:

They are peaceful shoaling fish, and ideal as filler fish. Because of their timid nature, they are easily picked on. Thus, never keep them with other aggressive fish species. In terms of how many fish can be in a 20 gallon tank successfully, larger schools can often become hyperactive, while small schools (under 4) can become aggressive.

  • Tank and Water Requirements:

Rasboras require water temperatures of around 70 – 82 F (21 – 27.7 ̊ C) and a pH of 5.0 to 7.7. You can try to mimic their natural habitat with some driftwood to increase tannins and plenty of aquatic plants.

  • What to Feed:

They are middle and bottom dwellers; thus, you will have to feed them sinking foods. Quality pellets flaked foods, or sinkable wafers are ideal. Similarly, brine shrimp, small worms, insect larvae, or daphnia make good proteins. Shredded blanched vegetables also provide a healthy snack. For tetra alternatives, they are one of the best fish for 20 gallon tank environments if you want something striking and different.

12. Checkerboard Cichlids (Dicrossus filamentosus)

Checkerboard Cichlids
Their colors are quite like the black and white squares of a checker or chessboard. Image from Flickr

A smaller South American cichlid with quite a peaceful temperament. They are ideal as a centerpiece or kept in groups for their schooling abilities. However, it’s advisable to keep a ratio of three or more females with one male.

  • Description:

They are stunning little fish, with elongated bodies. Their colors are quite like the black and white squares of a checker or chessboard. They usually reach around 3 – 4 inches (7.6 – 10cm) in size.

  • Origin and Natural Habitat:

They originate from shallow rivers in South America. Here they usually school in the bottom layers just above dead leaves and plant matter. When disturbed they will hide underneath the leaves.

  • Temperament and Behaviour:

For a cichlid, they are surprisingly peaceful and mellow. They also get along well with other peaceful tank mates.

  • Tank and Water Requirements:

Like their natural environment, they prefer more acidic black water. Higher temperatures of 79 – 86 F (26 – 30 C), and an acidic pH of 4.5 to 6.0 are suitable.

  • What to Feed

They are omnivores and bottom feeders, thus require sinking food. Nano Pellets and flakes are ideal. They also enjoy plenty of proteins such as live and frozen bloodworms, or brine shrimp. You could give the occasional shredded vegetable as a snack. In terms of the best fish for 20 gallon tank environments, they are less well known and very underrated.

Bottom Feeding Fish

13. Dwarf Corydoras Catfish (Corydoras hastatus)

Dwarf Corydoras Catfish
They naturally occur in the rivers and tributaries of Brazil. Image from Flickr

Dwarf Corydoras, also called Pygmy Corydoras are the perfect mini catfish for a 20-gallon tank. There are many different color variations and species available, and they are quite easy to keep. Because of their size and peaceful nature, they are perfect for community tanks. You can keep a single or small group with more females than males.

  • Description:

Naturally, they are a translucent silver grey, with a long horizontal stripe across their midsection. Though there are albino and a few other color variations available. They range in size between 1.9 centimeters (0.75 in) for males and 2.5 centimeters (1.0 in) for females.

  • Origin and Natural Habitat:

They naturally occur in the rivers and tributaries of Brazil. Here they rummage in the soft sand for food and occasionally borrow in the sand.

  • Temperament and Behaviour:

They are peaceful and do well in a planted tank with similar peaceful species. In terms of how many fish can be in a 20 gallon tank successfully, remember that bottom feeders should still be counted, even though they clean up the tank!

  • Tank and Water Requirements:

Corydoras thrive in a planted tank with soft sand or gravel substrate. However, keep in mind they do tend to burrow and dig up weaker plants. Cooler temperatures of between 22–26 °C (72–79 °F), and a pH of around 6.0 – 8.0 is ideal for them.

  • What to Feed:

They are bottom feeders and usually prefer live foods such as bloodworms, brine shrimp, and insect larvae or daphnia. Similarly, you can feed them nano pellets, freeze-dried tubifex worms, and sinking wafers.

14. Kuhli Loaches (Pangio kuhlii)

Kuhli Loaches
Kuhli loaches have a long thin body with yellow and black, or white and black vertical bars. Image from Flickr

Kuhli Loaches are quite fascinating little bottom dwellers and some of the best fish for a 20 gallon tank for algae cleaning. With their striped colors and long snake-like bodies they have a certain appeal. They will do well in a group of 5 – 6 in a 20-gallon tank. They are also ideal for beginners and reasonably easy to keep.

  • Description:

Kuhli loaches have a long thin body with yellow and black, or white and black vertical bars. They reach size of between 2.7 – 4 inches (7 – 10 cm).

  • Origin and Natural Habitat:

Kuhli Loaches are native to Indonesia. They are avid bottom feeders that mostly only come out at night. Though can be trained differently in captivity. They naturally occur in freshwater bodies which include lowland forest canals, hill streams, and peats.

  • Temperament and Behaviour:

Ideally, they are very peaceful and slightly shy. Try to keep them with similar peaceful communal fish.

  • Tank and Water Requirements:

Kuhli Loaches require slightly warmer temperatures around 24–30 °C (75–86 °F) and a more acidic pH of between 5.5 and 6.5.

  • What to Feed:

They are bottom-feeding omnivores. Feed them sinkable wafers and food, along with frozen and live bloodworms, and brine shrimp.

15. Panda Garra (Garra Flavatra)

Panda Garra
Panda Garra is a small fish reaching 3 inches (7.6 cm) in size. They are a greyish-yellow color with thick black markings, resembling that of a panda. Image from Flickr

The Panda Gara is a species that is not too well known by most. However, it is worth considering as a bottom-dwelling communal fish for your 20-gallon tank. They are moderately easy to keep, though suitable for someone with a bit of experience.

  • Description:

Panda Garra is a small fish reaching 3 inches (7.6 cm) in size. They are a greyish-yellow color with thick black markings, resembling that of a panda.

  • Origin and Natural Habitat:

They inhabit the bottom of Southeast Asian streams and rivers. They thrive in a more dynamic ecosystem with less vegetation.

  • Temperament and Behaviour:

They are active, but peaceful fish. However, they are not schooling, though it is best to keep a group of 5 or a single fish. They often end up squabbling if there are less than five.

  • Tank and Water Requirements:

Water parameters should remain clean and within pH ranges of 5.5 to 6.5., which is more acidic. They thrive in cooler temperatures of around 21–23 °C (70–74 °F).

  • What to Feed:

Because they are bottom dwellers, sinkable wafers are the most suitable. They also enjoy frozen or live protein-based foods. These include brine shrimp, daphnia, insect larvae, blood worms, or micro worms.

In Conclusion

As you can see the 15 best fish for a 20-gallon tank are not necessarily only fish that look good. They are carefully selected taking into account aquarium requirements, and their temperament. These species have much similar water parameter requirements and are mostly peaceful species that get along well.

Frequently Asked Questions

How many fish in a 20-gallon tank?
It all depends on the size and space requirements of the fish. You could safely house around 15 small fish species 1-3 inches (2-7 cm), in a 20-gallon tank. However, you cannot house more than three to four medium to larger-sized fish in a 20-gallon. Please do not follow the 1-inch size fish per gallon tip, this only pertains to small fish. Something like a large Oscar, could not be on its own in a 20-gallon tank.
Why Must I Not Overcrowd My Tank?
Overcrowding causes excess waste build-up and frustrates fish. Fish may fight with each other for space. You will also have to clean and change water more frequently.
Can I keep One Very Large fish in a 20 20-gallon tank?
Not really, a large fish still requires plenty of swimming space, even if it’s only one. You could, however, keep two or three Angelfish on their own, or some Ram species in small groups.
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