How Many Betta Fish Can Live in a 20-Gallon Tank? A Guide

Alison Page

Alison Page


how many betta fish in a 20 gallon tank

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Keeping and breeding betta fish is an incredibly popular hobby these days, so if you have a spacious 20-gallon tank, you might be wondering how many of these beautiful fish you can keep.

Can you keep multiple male Siamese fighting fish together in one tank? Do female betta fish fight? And what special adaptations do you need to make to your tank to accommodate more than one male betta?

Read this guide to find out how many betta fish can live in a 20-gallon tank and more!

Is a 20-Gallon Tank Large Enough for Betta Fish?

Bettas are generally considered nano fish and are often kept in small aquariums of around 5 gallons. In fact, I successfully kept one male betta and a few suitable companions in a 10-gallon tank, and there was plenty of space for him.

That said, wild bettas tend to adopt a territory of around 3 square feet, so if you can provide your fish with a larger tank, that’s even better, and 20 gallons is pretty much the perfect tank size.

Given that most species of betta fish grow to only 2 to 2.5 inches in length, they clearly don’t physically need a huge tank.

However, these extremely territorial, aggressive fish don’t appreciate living in cramped quarters with lots of company. In their natural habitat, betta fish are solitary creatures, only interacting with other bettas when spawning or during encounters with rival males. Bearing that in mind, you can see that a 20-gallon tank provides ample space for betta fish.

How Many Betta Fish Can Live In a 20-Gallon Aquarium?

Several critical factors determine how many betta fish can live in a 20-gallon fish tank, and we’ll discuss them below.

Male or Female?

The sex of your betta fish is crucial when determining how many of these gorgeous fish you can keep in your 20-gallon betta fish tank.

Both sexes are somewhat territorial, although, in my experience, males are much more aggressive than females when it comes to protecting their adopted patch. In fact, if you try to put more than one male betta in the same tank, a fight is pretty much guaranteed, and these fish will fight to the death in defense of their territory.

However, I’ve kept small groups of up to five female betta fish in the same tank several times without incident.

In fact, you shouldn’t keep two female bettas together because one will probably try to bully the other. However, keeping a group of females tends to prevent that from happening.


So, now you know that you can’t safely keep more than one male betta fish in the same tank, no matter what size aquarium you have.

However, don’t despair! It is possible to keep multiple male bettas in one tank if you use dividers to split the tank into separate compartments for each fish.

As you’ll know, if you use a mirror to exercise your betta and encourage him to flare, even the sight of another betta fish through glass could trigger an attack. Therefore, you must use opaque dividers extending right down the tank bottom. That way, the fish can’t see each other and are unable to swim underneath the divider.

The number of dividers you use depends on how many male Siamese fighting fish you intend to keep in your 20-gallon tank. Most hobbyists use three dividers to accommodate four male betta fish in a 20-gallon aquarium, which is fine, provided each fish has at least a 5-gallon enclosure.

Potential Issues

Using dividers presents the aquarist with a few challenges.

  • Your filtration system must be powerful enough to pull water through each section and right around the entire tank.
  • The dividers must fit properly so the bettas can’t get into each other’s individual compartments.
  • You must be extremely diligent when it comes to keeping each compartment clean and maintaining consistent water parameters throughout the whole tank.
  • It can be difficult to maintain a constant, stable water temperature in a tank containing dividers. Bettas are vulnerable to temperature shock, which can be fatal, so you must have a heater that’s powerful enough to keep the water warm enough throughout the tank.

However, if those challenges don’t faze you, keeping more than one male betta in a 20-gallon tank could be an option for you.

Tank Maintenance

The more fish you keep, the more important it is to keep your fish tank clean and well-maintained. That’s because more fish waste and leftover food can accumulate quickly, producing ammonia and other harmful chemicals as it decomposes.

In a busy tank, you’ll need to carry out weekly water changes and keep on top of filter maintenance. If you keep live aquatic plants, you must trim overgrowth and dead leaves as required.

Aquarium Decoration

Wild betta fish live in a heavily-vegetated natural environment, so you must try to recreate that as much as possible in your betta tank. These fish also need plenty of hiding places like caves and rocky overhangs that they can claim as territory. Of course, that’s tricky to achieve in a tank with dividers.

In a tank containing a betta sorority, you have more space and scope for things like driftwood, pebbles, smooth rocks, and plenty of plants to create a beautiful tank.

Just bear in mind that a decorated aquarium might be a wonderful sight, but everything you put in it takes up valuable swimming space for your fish.

How Many Female Bettas Can Live In a 20-Gallon Tank?

how many betta fish in a 20 gallon tank

If you want to keep a female betta sorority tank, I suggest keeping between four and five fish.

Remember to provide the fish with lots of plants and hiding places where they can shelter and feel safe.

Female bettas do tend to squabble amongst themselves occasionally, so giving them somewhere to take refuge is essential for a harmonious community setup.

Male Betta Fish

You can keep one male betta fish in a 20-gallon tank. This tank size gives plenty of space for the fish and lots of attractive decorations, so it’s a win-win.

If you want multiple males, you must use dividers, and you could have four or five fish.

Whether you keep one individual or several fish separated by dividers, you must provide them with plenty of hiding spots, resting places, and plants.

Male bettas like to build bubble nests, so floating plants are a great idea, provided you leave enough space for the fish to access the water’s surface to breathe.

Can You Keep Male and Female Betta Fish Together?

Although it might seem like a good idea to put one male and one female betta fish together, that’s often a recipe for disaster.

Male bettas can be extremely aggressive toward one solitary female, nipping at them or pursuing them around the aquarium.

This stresses both fish, sometimes leading to injuries and other health problems. So, rather than putting one fish of each sex together, it’s usually best to keep them apart.

That said, I kept a sorority of bettas with one male with no problems at all. Perhaps the fish’s behavior simply depends on the personality of the individual male and the dominant female.

Avoid Overstocking the Tank

If you decide to keep just one male betta in your 20-gallon tank, you might want to add a few suitable tank mates to keep him company.

Although male bettas are solitary creatures, these are intelligent, curious fish, and they do appreciate the mental and physical stimulation provided by a few peaceful tank mates.

Bottom-dwelling fish species can make ideal tank mates, including Corydoras catfish and small plecos, which usually work well, as do peaceful fish that live in the middle region of the water column.

Be aware that some tetra species, such as Neon tetras, can be nippy and could hassle the betta, and large, aggressive fish might cause problems by bullying the betta.

Usually, larger shrimp and ornamental snails make excellent tank mates for betta fish, keeping themselves to themselves and providing a valuable cleanup crew service as a bonus.

Final Thoughts

Did you enjoy our guide to how many betta fish can live in a 20-gallon fish tank? If you did, remember that sharing is caring, and hit the Share button above!

Male bettas are highly aggressive tropical fish that cannot live together unless you use opaque tank dividers to create separate habitats for them. However, you can safely keep a small betta sorority or a single male betta with a few suitable tank mates.

Do you keep multiple bettas in one tank with dividers? Tell us how your fishy friends are doing in the comments box below!

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