How Many Angelfish In A 40-Gallon Tank? Will They School?

Dec 9, 2021

How Many Angelfish In A 40-Gallon Tank?

If you’re just dabbling in the angelfish-keeping hobby, I’d say a 40-gallon tank is an ideal size to start with. It’s neither too big nor too small. It’s just the right size to offer some room for mistakes without being too overwhelming to manage. But how many angelfish in a 40-gallon is possible? Will they even school in a 40-gallon tank? 

In this blog, I won’t just tell you about a scientific, mathematically correct answer for your query but also let you in on a little secret formula to calculate the stocking number for practically any given tank size! And I’ll also discuss a few stocking ideas! 

So, let’s get rolling! 

How Many Angelfish In A 40-Gallon Tank? 

You can house only 2-4 angelfish (preferably 2 pairs) in a 40-gallon tank. Angelfish grow to a decent size, reaching up to 6 inches on average. Plus, they’re cichlids – so, they’re inherently aggressive and territorial. Therefore, you should be prepared to separate the pairs if needed when the time comes. 

Usually, the duo tends to get super intolerant of their tankmates once the pairs are formed. I guess it’s got something to do with survival or parental instincts! 

So, if the situation gets out of your hands – constant nipping, lip-locking, and chasing – and you think lives are in danger, intervene and relocate the victimized fish or fishes! 

However, from my personal experience and that of many others I read on forums, 4 angelfish in a 40-gallon tank are manageable as long as there are enough hiding places in the tank, and the resources aren’t scarce. 

Will Angelfish School In A 40-Gallon Tank?

Most probably, no. Angelfish aren’t really keen on schooling, to begin with. However, watching them form territories and hierarchies and compete for dominance can be pretty engaging! 

So, let me share the secret little formula. 

Recommended Readings!

How Many Angelfish In A 29-Gallon Tank? Do They Shrink In Small Tank?

How Many Angelfish In A 75-Gallon Tank? Use This Golden Rule!

How Many Angelfish In A 55-Gallon Tank? Use This Formula!

Easy Stocking Formula For Tropical Fish 

Credits: Jenly (Creative Commons license)

The formula I’ve been babbling about all this time was given by a veteran aquarist and author Dick Mills in his book You and Your Aquarium. The book first came out in the 1980s. 

However, the formula is still used widely to date by both seasoned and newbie hobbyists alike. 

The instructions go something like this:

You have to allocate at least 12 square inches of open tank surface for every inch of a tropical fish’s body. 

You’ll need to ensure 30 inches minimum for cold, freshwater fish – and for tropical marine fish, you need to provide 48 inches. 

The steps involved are quite simple. You can find out the correct stocking number in just 3 simple steps. 

Step 1: Find the tank’s surface area (L x w)

Step 2: Find the total inch of fish the tank can accommodate (surface area / 12)

Step 3: Find the total number of fish the tank can accommodate (answer from step 2 / height of the fish)

So, let’s calculate the answer for a 40-gallon high tank. 

Note that it’s essential to get a 40-gallon high tank instead of a 40-gallon long or breeder tank since these fish grow pretty tall. 

A 40-gallon high tank’s dimensions are: 36” x 13” x 20” (L x W x H)

The tank’s surface area = L x W

= 36 x 13

= 468 

Total inches of angelfish a 40-gallon high tank can accommodate = surface area / 12 

= 468/13

= 39 inches 

Now, let’s assume the angelfish’s height is 10 inches. In captivity, these fish usually grow 8-10 inches tall. 

So, 

Total number of angelfish a 40-gallon high tank can house = 

Total inches of angelfish a 40-gallon high tank can accommodate / angelfish’s height 

= 39/10

= 3.9

A 40-gallon high tank can house 3.9 angelfish. You can round it off to 4. 

Hence, we can conclude that a 40-gallon high tank can house 4 angelfish that are around 6 inches long and 10 inches tall. 

3 Different Kinds Of 40-Gallon Tanks 

Note that not all 40-gallon tanks are made equal. 

They at least come in 3 different dimensions. 

Tank TypeDimensions (L x W x H)
40-gallon high 36” x 13” x 20”
40-gallon long 48” x 12” x16”
40-gallon breeder  36” x 18” x16”

And as I stated above, angelfish need tall tanks to accommodate their tall, erect fins. Especially steer clear from a breeder tank since they’ve been designed to have a lower profile so breeders can easily access their fish. 

Recently, I’ve been adding a new segment in most of my blogs, where I pool in relevant and useful answers left by real hobbyists on different forums. I do so to help you save time, find all the answers you need on one platform, and make an informed decision. 

So, let’s look at what people have to say! 

How Many Angelfish In A 40-Gallon Tank? Real Answers By Real People

All the opinions expressed below purely belong to the respective author.

“I think 4 at the most, but that might be pushing it. You might have a problem when they pair up. I’m not too sure.”

“I currently have two with 4 blue gouramis and a rainbow shark (and a few other less interesting fish).”

“In my current 40-gallon tank, my mom used to keep 4 angelfish alongside some mollies and neons. Everyone got along peacefully.”

“I had 6 angelfish in a 37-gallon tank. As they grew, 2 paired up, and now I’m only left with 2 :(. “

“You can easily start with 4 dime to nickel-sized young angelfish and let them mature. See who or how many pairs. Then you’d want to remove 2.”

“If over quarter-size, give them 5 gallons per angelfish. If over silver dollar-sized, give them 7 gallons per fish. And once they mature and start breeding, it’s best if you give them 10 gallons each.”

So, as you can see from the quotes above, there’s no one rule etched in stone. The stocking number differs from one hobbyist to another. In the end, it all boils down to your preference, your fish’s temperament, and how okay you’re with one or two deaths from brawls. 

Tankmates For Angelfish In A 40-gallon Tank

I’m not too sure if it’s a good idea to add tankmates to a 40-gallon angelfish tank that already has 2 breeding pairs. These fish can get tremendously mean when guarding their eggs and young ones, as I mentioned above. 

So, if you’re going to add fish to their tank, make sure the fish are almost the same size as the angelfish, and they can hold their own against these feisty cichlids. 

From what I scoured from at least a half dozen forums, here’s a list of possible tank mates I came up with. 

  • Dwarf gouramis 
  • Albino corydoras 
  • Bronze corydoras 
  • Sterbai corydoras 
  • Adolfoi corydoras 
  • Columbian tetras 
  • Lemon tetras 
  • Rummy nose tetras 
  • Bristlenose plecos 
  • Bolivian rams
  • Kuhli loaches 
  • Swordtails 

3 Things To Remember When Stocking Angelfish 

Angelfish are ubiquitous in all community aquariums. So, it’s easy to think they’re compatible everywhere and with almost everyone. But this isn’t always the case. The 3 things you need to remember before you bring them home are that they lead a long life, can grow quite big, and have an aggressive side to them. 

Angelfish’s Age 

Angelfish enjoy a pretty long lifespan. Even in captivity, they can easily live for around 10 years on average. Now this means that you have to care and provide for them for more than a decade or so. 

Over time, you will inevitably have to upgrade the tank, relocate the fish, or give them away. So, always first make sure to evaluate what lengths you are willing to go to raise these fish.

Angelfish’s Size 

An average angelfish grows over 6 inches long and 10 inches tall. That may not be too big in the Amazonian river basin, but it is in an enclosed system like tanks. 

Therefore, while calculating the stocking number, you should always consider the fish’s maximum potential size. 

Angelfish’s Temperament 

Angelfish aren’t as aggressive and hostile as convicts and oscars. However, they can still get pretty mean when things don’t go their way. 

This is especially true during spawning when they wouldn’t even mind bullying the perceived “enemy” to death. 

Thus, there’s a good chance that you will have to upgrade the tank or relocate some fish here and there to manage an angelfish’s aggression. 

Final Words: How Many Angelfish In A 40-Gallon Tank?

Here’s a short recap for you. 

You can add around 4 medium-sized angelfish in a 40-gallon high tank. Remember, I said a high tank – not a long tank or a breeding tank. 

You need to ensure at least 12 square inches of space for every inch of the fish’s body, according to master aquarist Dick Mills. And as you saw, when we calculate using this formula, the ideal number that we get will be 4. 

However, you’d still have to take this info with a pinch of salt. 

If the fish start getting too territorial and aggressive towards each other, you will have to remove and relocate them! 

Recommended Readings!

10 Gallon Fish Tank Weight | How Many Fish Can It Hold?

How Many Cichlids In A 75-Gallon Tank? Mbunas, Peacocks And South American

How Many Cichlids in a 55-Gallon Tank? Use This Simple Formula!

How Many Cichlids In A 40-Gallon Tank? Cichlid List For A 40-Gallon Tank

rohit gurung author at urbanfishkeeping

About Rohit Gurung

My never-ending love and fascination with Aquascaping started when I received a red-eared turtle for my 10th birthday.

Apart from researching and writing, I spend hours gazing at my 3 turtles. And yeah, I bask alongside them too.