How Many Cichlids in a 40 Gallon Tank? (Detailed Guide)

A 40-gallon aquarium is a very popular size for those who start dabbling in fish-keeping.

The standard dimensions of this aquarium are 36” x 18” x 16”. This is a reasonable cichlids tank size for beginners to raise a small group of cichlids. However, keeping cichlids is difficult as they are aggressively territorial. That means they hardly live in peace and get along with other fish.

How many cichlids in a 40 gallon tank? Using the thumb rule, there is one inch of adult fish for every two-gallon water. This means you can have about 20 inches or 5 – 7 cinchlids in a 40-gallon breeder aquarium.

How Many Cichlids Should You Put in a 40-gallon Tank?


Following the 1-inch fish for 2 gallons of water rule, you can have up to 12 dwarf cichlids or 6 medium-sized cichlids in a 40-gallon aquarium. A good filtration system is necessary to hold this number of fish effectively.

If you want to house several cichlids, having 6 or 7 of each species is acceptable. Don’t let aggression levels get too high!

In general, each type of cichlid has its size. You better know the size of each species well to get the right number of cichlids per gallon.

Here is the list of the most popular cichlids with detailed size information and suggested fish numbers. It can be helpful if you are looking for 40 gallon breeder stocking ideas.

Types of Cichlids

1. Jewel Cichlids in a 40-gallon tank


A full-grown size of Jewel Cichlids is no more than 6 inches. Typically, each of them requires a minimum of 30 gallons. Every additional will need 10 gallons extra, so you can house 2 Jewel in a 40 gallon cichlid tank.

Some people said a 36 gallon tank is the minimum, but 40 gallons is advisable to give them extra space.

Jewel Cichlids are super aggressive. You need to be careful when choosing tank mates. Some cichlids keepers have tried to pair them with African cichlids, and it luckily works. This is a good example of cichlid tank ideas!

2. Demasoni Cichlids in a 40-gallon tank

Demasoni cichlids are considered small cichlids that can fully grow to 4 inches long. With this size, a 40-gallon aquarium can hold 8-12 of these together. There should be at least 3 females for every Demasoni male.

Make sure you keep over 5 Demasoni cichlids to scatter the bullying behavior of the dominant male. In contrast, the subdominant male can get bullied until dying.

Cichlid keepers also need to frequently do water changes and make sure a good set-up filtration system.

3. Electric Yellow cichlids (Yellow Lab) in a 40-gallon tank


The average Electric Yellow cichlid’s size when fully grown is 4 inches, making them one of the ideal African cichlids for small tanks. Typically, a 40-gallon cichlid tank should only keep up to 8 Yellow Lab to avoid overstock that can cause territorial behavior.

Basically, Electric Yellow cichlids are not an aggressive species. They can only show some aggressive behaviors during the spawning season. So, keeping them in a community aquarium is fine as long as you give them enough space.

The ideal companions for Yellow Lab are some Mbuna cichlids species, such as Keyhole cichlids or Pseudotroopheus.

4. Acei Cichlid (Yellow Tail Acei) in a 40-gallon tank

An adult Acei Cichlid can grow up to 5 inches, some male fish can even reach 5.9 inches. It only takes over a year for them to grow to full size.

Although it’s ok for a 40-gallon tank to keep up to 5 Yellow Acei Cichlids, a 55-gallon tank seems to be much more comfortable to keep this number of fish.

Remember, there should be only one male with 3-4 females in a group. If you have two males, they will fight for dominance to the death. The Yellow Tail Acei is not an aggressive species, but they do show social behaviors.

5. Ram Cichlids in a 40-gallon tank


Ram is one of the South American cichlids that can grow up to 3 inches in size. The ideal number of these fish for a 40-gallon aquarium is 4.

You need to know that Ram cichlids love to be kept in a pair. So 2 pairs are a reasonable number for your tank.

Unlike other cichlid species, they are peaceful. Therefore, you don’t have to worry about the males fighting each other. Their size and contrasting colors make them a great addition to any aquarium.

6. Peacock cichlids in a 40-gallon tank

Peacock cichlids normally grow up to 6 inches long. Peacocks are indeed just mid-size fish. You should only keep 2-3 of them. They are aggressive territorial species that will go crazy in a small tank.

Although there is not much difference between a 40 and 45-gallon aquarium in size, 45 gallon tank still gives Peacock cichlids extra room.

Generally, it’s hard to keep Peacocks with other fish as they are aggressive. So finding them some sociable tank mates such as Dwarf Chain Loach or Plecos may be a good idea.

7. Convict Cichlids in a 40-gallon tank


An average full-grown Convict cichlid is around 5 inches. Some of the males can reach 6 inches long. In general, a 40-gallon aquarium should only keep up to 3 of them.

According to some aquarists, a pair of Convict cichlids should be kept in a 30-gallon tank at least. Each addition will need extra 10 gallons. Generally, the ideal tank for raising a Convict is 50 gallon tank. The larger, the better.

Convict cichlids are mean ones, but they will not show aggressive behaviors toward others if they have enough space. However, finding them a compatible tankmate is still challenging.



What water parameters do Yellow Lab cichlids need?

Here are some water parameters you need to notice when keeping Yellow Lab Cichlids:

  • pH level: Most Yellow Lab cichlids are happy at pH levels between 7.2 to 8.8.
  • Water hardness: The general level of hardness should be maintained between 10 and 20 dGH.
  • Water temperature: The water temperature should be between 22 – 28°C ( 72 – 82°F).
  • Partial water change: Perform a 10% to 20% water change every week to keep the water quality.
  • Nitrite and ammonia: Nitrite and ammonia level should be ZERO all the time along with good water movement.
  • Nitrate levels: Nitrate levels need to be preferably under 40 ppm.

What ratio male to female cichlids should I have in a 40 gallon aquarium?

When it comes to keeping cichlids in a 40-gallon tank, the male/female ratio should be 1/4 (1 male for every 4 females) in general. This ratio will not only prevent male aggression but also protects the female fish.

However, the exact ratio mostly depends on the type of cichlids. Some species need a higher female ratio, some are fine with 2.

Yellow Lab, for example, is recommended to have a 1/2 ratio (1 male for 2 females), while Peacock’s male/ female ratio is 1 male for at least 3 females.

While a 1/4 ratio may not seem necessary for some cichlids in a 40-gallon tank, this is a reasonable general ratio to avoid casualties.


How many cichlids in a 40-gallon tank? Having around 6 mid-sized cichlids is the most suitable number for a 40-gallon tank. Most cichlids are aggressive so it is a bit tricky to find them tankmates, but it’s not impossible!

Finally, a 40-gallon aquarium is a great size tank for starters that can hold a small group of cichlids. However, before adding any new fish, you need to know their size and behavior well to calculate the exact number of fish and prevent fighting.