how many betta fish in a 20 gallon tank

How Many Betta Fish in a 20-Gallon Tank? Let’s Find Out..

Sharing is caring!

In my opinion, a 20-gallon tank is an excellent size for a betta tank. It allows plenty of swimming space, and also the possibility of adding schooling tank mates, too.

Male bettas can only be kept in the same tank if it has dividers, and a divided betta tank can accommodate up to 4 males.

But what about keeping female bettas together, and which tank mates are the best for a 20-gallon betta tank? Let’s find out!

Why Male Betta Fish Should Never Be Kept Together

Male betta splendens are so aggressive, they’ve even earned themselves the name ‘Siamese fighting fish’. In Asia, males are sometimes pitted against each other in cruel contests where they fight to the death.

Even in a larger tank with a 20-gallon capacity, male bettas must never be kept together. Doing so would likely result in serious injuries at the very least.

So, keeping two males in the same tank is never an option – without a divider, that is.

What Is a Betta Tank Divider?

Betta tank dividers are permeable barriers that divide a single fish tank into multiple living compartments so that the fish can’t reach one another. There’s no limit to the number of compartments possible, but two or three chambers are the most common setup.

Betta tank dividers are typically made from some kind of permeable glass, plastic, or mesh barrier that prevents males from attacking one another.

A good enough concept, but how well do betta tank dividers work in reality?

Advantages of a Betta Tank Divider

The obvious advantage of a betta tank divider is that it allows you to keep multiple male bettas in a single tank. It’s also cheaper than buying two betta tanks.

But there are some hitches, too!

Problems With Betta Tank Dividers

A potential problem in betta tanks with a divider is that your male bettas may still flare and spar with one another from each side of the barrier, causing a lot of stress and even minor injuries.

Another common issue is uneven water circulation between the chambers. If there is only one filter, the compartment with the filter will likely receive too much water flow, whereas the other chambers can become stagnant. Either of these can be seriously stressful and harmful for your bettas.

Finally, people will sometimes try to cram too many chambers into one small tank. Cramped compartments of less than 5 gallons are simply too small for betta fish to remain happy. In such a tight space, betta fish are very likely to die prematurely.

How to Make a Betta Tank Divider the Right Way

Just because there are some potential drawbacks to betta tank dividers, it doesn’t mean that we need to write them off altogether!

As well as making sure that each betta has 5 gallons of swimming space, there are 2 more fundamental principles for how to make it work:

Keep Your Bettas Out of Sight From Each Other

Firstly, make sure that your betta fish can’t see each other between the divider so they don’t flare and bicker with one another from each side.

For this, you’ll need to make the divider from some type of fairly opaque material such as colored, water-safe PVC, or acrylic. A dense, dark-colored mesh may also be sufficient to keep the fish out of sight from each other.

Place a Sponge Filter in Each Chamber

The problem with power filters in a divided tank is that the flow will be too strong in the first chamber, and too weak in the others.

To solve this, try using small, low-powered sponge filters in each chamber. Sponge filters are incredibly cheap, and you don’t even need to buy separate air pumps – simply use a reliable one with dual outlets like this!

Uniclife 64 GPH Aquarium Air Pump with Dual Outlets Adjustable Quiet Fish Tank Air Pump with Air...
  • Steady Output: Max Air Flow Rate: 64 GPH; Pressure: 0.016 MPa; Power: 4 W. Perfect for aeration in 10 - 100 gallon fresh water and marine aquariums.(The data is measured with experimental equipment and may deviate slightly from the actual data. The air volume may be insufficient due to the blocked air intake cotton. Please replace the cotton yourself if the air volume is insufficient.)
  • Adjustable Air Flow: Feature a rotary knob to control the amount of air for dual outputs, allowing for your desired air flow to fully oxygenate your fish tank.
  • Quiet Operation: The pump emits 25 dB sound under the “Low” mode and maximum 45 dB noise like the hum of a refrigerator under the highest air flow.

How Many Male Bettas Can You Keep in a 20-Gallon Tank?

Since each male betta fish should have at least 5 gallons of free swimming space, you could keep up to 4 bettas in a 20-gallon aquarium, with 3 dividers. You could also keep 3 bettas with 2 dividers, or 2 bettas with a single divider.

Remember that your bettas will be grateful for the extra swimming space!

Keeping a Female Betta Sorority in a 20-Gallon Tank

While male betta fish are extremely aggressive towards one another, females are rather more relaxed fish and are sometimes kept together in ‘betta sorority tanks’.

This doesn’t mean that females are altogether docile though – they’re more than capable of picking fights with one another, too!

Opinions are divided over whether female betta sorority tanks are worthwhile or even ethical. Because these fish can still fight with each other, bullying is commonplace, and that can lead to unnecessary casualties.

The Minimum Number of Female Bettas in a Sorority

To provide the most harmonious setup, it’s recommended to keep no less than 5 females together. This is because having more fish helps to divide up and disperse aggression between female fish.

If you were to keep an aggressive dominant female with just one or two others, the weaker fish would simply receive too much aggression and would likely become overwhelmed and stressed. Constant harassment could lead to injuries and even death.

Is a 20-Gallon Tank Big Enough for a Female Betta Sorority Aquarium?

Female betta fish are slightly smaller than males and therefore can manage with slightly less swimming space. So while 5 gallons is the minimum for male betta fish, 4 gallons is acceptable for females.

This means that a 20-gallon tank is enough space for 5 female bettas – the minimum number that’s safe to keep together.

In short, I’d advise 20 gallons as the smallest tank size for a betta sorority if you only wanted to keep betta fish. If you wanted a few tank mates like corydoras catfish or some kuhli loaches, you’d need at least a 30-gallon tank.

Making a Peaceful Sorority Betta Tank

As well as never keeping female bettas in groups of less than 5, I’d recommend providing the girls with plenty of plants and hiding places. Since each fish will assert its own territory and pecking order, it’s important that each female has a place to escape any tense encounters.

I’d also advise keeping all water parameters, water temperature, and diet at optimum levels to keep your female bettas happy. If they become stressed, they’ll turn into aggressive fish, and that’s why betta sororities are best left to advanced fish keepers only!

Why Male and Female Bettas Shouldn’t Be Kept Together

Not only are male bettas incredibly territorial towards each other, but they can be very aggressive towards females, too. This means that they should never be kept in the same tank, except for a very brief moment for spawning together.

Breeding bettas in captivity is a very delicate and tense affair that requires expert knowledge and experience to get right. Oftentimes you have to separate the fish before someone (usually the female) gets hurt.

Is a 20-Gallon Tank Suitable for Breeding Betta Fish?

how many betta fish in a 20 gallon tank

Female bettas typically lay between 30-100 eggs in each batch, but they can occasionally lay several hundred. This means that a 10-gallon tank is often considered too small for a betta breeding tank, and a 20-gallon tank is the preferred choice.

The Best Tank Mates for a 20-Gallon Betta Tank

A 20-gallon fish tank is an excellent size for betta fish because it allows you to keep many other interesting species of fish alongside your betta.

Whereas in a 10 or 15-gallon aquarium schooling fish tend to scatter and ‘hover’ around, a 20-gallon tank allows them to swim about in tight schools just as they would in the wild.

Here are some of the best choices:


Rasboras might just be the ultimate open-water schooling fish to keep in a betta fish tank. Not only are they small and docile, but they also come from the same rice paddy and forest pool habitats as betta fish. This means they enjoy the same water conditions and are compatible in most ways.

If you’re a beginner, Harlequin Rasboras make the best choice. These fish are incredibly peaceful, hardy, and easy to care for. For those with more experience, you could also try Scissortail Rasboras or Dwarf Rasboras.


Tetras can be slightly more tricky to keep with bettas since they have a reputation for nipping fins, but this depends a lot on the species and tank conditions.

Serpae tetra, Blue tetras, White spot tetras, Buenos Aires tetras, Blind cave fish, and Black widow tetra are all well-known for nipping fins and should never be kept with betta fish.

Neon tetra, Rummy nose tetra, and Ember tetra all tend to be more peaceful, but can still nip fins when stressed. The secret is to keep them feeling relaxed and calm by offering them a densely planted tank with plenty of hiding spaces and excellent water quality.


Some people have successfully kept guppies with bettas, but their bright colors and long fins can sometimes trigger the fighting instinct in betta fish to attack them.

Better choices are platies and smaller swordtails, but keep a close watch on the situation to make sure that fin-nipping or fighting doesn’t break out.

Bristlenose Pleco

Whereas many pleco species such as common plecos and sailfin plecos get way too big to keep in a 20-gallon aquarium, bristlenose plecos are different.

Because bristlenoses only grow up to 3-5 inches long, they make one of the best algae eaters for a 20-gallon tank. They are also bottom-dwelling, peaceful fish that will hardly notice the presence of your betta.

Kuhli Loaches

Kuhli loaches are some of my favorite fish, period. Their beautiful patterns and quirky personalities make them a fascinating addition to most tropical fish community tanks.

Given some rocks and caves, kuhlis are also excellent at hiding, which can come in handy when sharing the tank with a grumpy betta! These social fish should always be kept in groups of 5 or more.

Corydoras Catfish

Cories are one of the ultimate betta tank mates for three great reasons: They’re incredibly peaceful, They occupy the bottom layers of the tank where your betta rarely goes, and they do an excellent job of keeping the fish tank clean.

Just be aware that cories need to be kept in schools with other members of their species to be happy, so never keep them in groups of less than 5 or 6.

Freshwater Shrimps

Cherry shrimp, ghost shrimp, and Amano shrimp all make peaceful tank mates for betta fish, and, like cories, they do a sterling job of keeping the tank clean.

Growing up to 2 inches long, Amano shrimp are one of the largest of the most commonly kept aquarium shrimps and therefore stand a better chance of resisting any aggressive behavior from your betta.

They are also some of the best algae eaters, and unlike the others, don’t breed in freshwater, so will never overpopulate your aquarium.

Aquarium Snails

Freshwater snails make some of the best algae-eating tank mates for betta fish, but note that most aquatic snails can breed in freshwater and can therefore quickly overrun a 10-gallon aquarium!

Nerite snails are one of the best choices because these beautiful black and white striped snails don’t eat aquarium plants and don’t breed in freshwater. With a shell of up to an inch in diameter, they’re also large enough to fend off all but the most ferocious betta fish!

Warning: No Tank Mate is Safe From an Aggressive Betta Fish!

While a 20-gallon tank offers very good chances of keeping other fish in harmony with your betta, it must be stressed that the temperament of each betta varies wildly between individuals!

Although some types of fish are better betta tank mates than others, there is no guarantee that any species will be safe from the fiercest fish.

Some bettas are so aggressive, they’ll attack anything that moves, including any tank mates, their owner’s hands, and their own reflection! Even the biggest, toughest snails like mystery snails aren’t safe from a raging betta, meaning you may have no choice but to keep him in his own separate tank!


A 20-gallon tank is a perfect tank size for betta fish. It offers them more swimming space and a greater selection of tank mates. It’s also the minimum tank size for keeping an all-female betta sorority together.

Male betta fish, on the other hand, should never be kept together without well-devised tank dividers.

To keep a female sorority with other tank mates, consider a 30-gallon aquarium.

Sharing is caring!

Leave a Comment

Your email address will not be published. Required fields are marked *