How Many Angelfish In A 20 Gallon Tank?

A 20-gallon tank is not large enough for keeping angelfish long-term. Angelfish are large, tall fish, and a 20-gallon tank would not provide enough swimming space for one fully grown angelfish. The tank must be at least 18 inches high to accommodate their long fins. 

If you are breeding angelfish, you can temporarily keep a male and female pair in a 20-gallon high tank. However, a pair of angelfish need at least a 29-gallon tank to live in permanently. Without enough tank space, fish become stressed, and this can lead to health problems and a shortened lifespan.

Can You Keep A Single Angelfish In A 20 Gallon Tank?

Unfortunately, you cannot keep angelfish in a 20-gallon tank permanently. This is just not enough space for these big, showy fish.

The general rule for figuring out how much tank space you need for different fish is 2 gallons per inch of fish. For example, if an angelfish is 6 inches long, it requires 12 gallons of tank space.

Therefore, in theory, you can keep a single angelfish in a 20-gallon tank, but this is far from ideal for the fish!

Angelfish are social animals that live in small groups in the wild. It is not advisable to keep just one angelfish. The isolation is very distressing for them, and it will significantly decrease their lifespan.

Can You Keep Two Angelfish In A 20 Gallon Tank?

Again, you can, theoretically, keep a pair of angelfish in a 20-gallon tank. But this is far from ideal for these fish. Expert aquarists strongly advise against keeping two angelfish in a 20-gallon tank permanently.

20 gallons is not enough space for these large fish to swim around. They may be able to survive in a 20-gallon tank, but they will not thrive.

Two Striped Angelfish Facing Each Other

How Many Angelfish Can You Keep In A Tank?

Below are guidelines for how many angelfish you can keep in a single-species tank:

  • A 30-gallon tank can house 2 mature angelfish or 5 angelfish fry
  • A 40-gallon tank can accommodate 3 adults (1 male, 2 females) or 7 fry
  • A 55-gallon tank can house 4 adult angelfish (1 male, 3 females) or 10 fry
  • A 75-gallon tank accommodates 5 adults (1 male, 4 females) or 10 fry
  • A 90-gallon tank is fine for 7 adults (1 male, 6 females) or 12 fry

How Large Do Angelfish Get?

Angelfish are tiny when you buy them as juveniles from the aquarium shop, so it looks like a 20-gallon tank can work for a small group of them.

However, mature angelfish are relatively large aquarium fish. They have a long, tall body shape, and their dorsal fins are very long.

Generally, angelfish reach around 6 inches in length when they are fully grown. Mature angelfish measure about 8 inches tall, including their fins.

Altum angelfish grow even larger. They reach about 7 inches long and 10 to 13 inches tall when they are fully grown.

Angelfish Need A High Tank

Because of their height, angelfish require a tank that is taller than it is long. You need a tank that is at least 18 inches tall to accommodate their long fins.

If angelfish fins constantly drag against the tank substrate because there isn’t enough space for them, they can develop infections like fin rot.

What Is The Smallest Possible Tank Size For Angelfish?

Considering their mature size, angelfish need a spacious tank to live happily. They must be kept in pairs, so the minimum tank size for two angelfish is 30 gallons.

It is okay to keep 4 young angelfish in a 30-gallon tank or 5 or 6 juveniles in a 55-gallon tank, but you must be prepared to remove some of them as they grow.

Remember that in a community tank, angelfish require double the amount of tank space than in a single-species tank.

If you want to keep a pair of angelfish in a community tank, you need a 55-gallon tank at least. This will ensure that they have plenty of space to have their own territory in the tank.

Angelfish in an overcrowded community tank can be aggressive towards their tank mates.

A 20 Gallon Tank For Breeding Angelfish

One case when it is okay to keep a pair of angelfish in a 20-gallon tank is when you want to breed them. Remember, it must be a 20-gallon high tank!

It is always a good idea to temporarily remove breeding pairs of angelfish from your main tank and put them into a separate, smaller tank because angelfish are particularly aggressive during the breeding season. Removing breeding pairs helps to keep the peace in your tank.

What Happens If Angelfish Do Not Have Enough Tank Space?

Living in overcrowded conditions or in a tank that is too small is bad for angelfish’s health. When these fish do not have adequate space in their tank, they become stressed.

Stress negatively affects fish’s health. Stressed fish are far more susceptible to pests and diseases, and they do not live for as long as they should.

Angelfish have surprisingly long lifespans. They can survive for 8 to 10 years in a tank! However, this is only possible if they have enough tank space and enjoy optimal living conditions.

Ideal Tank Conditions For Angelfish

Apart from having the right size tank for the number of angelfish you have, you need to get a few other factors right to keep your angelfish thriving.

The water parameters are important. Angelfish need warmer water, between 78- and 86 degrees F. 82 degrees F is ideal for breeding angelfish. The pH can be between 6 and 8.

High water quality is essential for keeping healthy angelfish. Ensure your tank has a powerful enough filter and pump. There should be no build-up of toxins, and oxygen levels should stay high.


If you wish to keep some beautiful angelfish, you must have a tank that is larger than 20 gallons. A 20-gallon tank is just not enough to accommodate these large, active fish. The minimum tank size for a pair of angelfish is 30 gallons.