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

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

I have a 75-gallon angelfish tank in my study. I follow a certain formula shared by a veteran aquarist to come up with the right stocking number. So, I thought, why not share it with you guys! Without further ado, let’s find out how many angelfish in a 75-gallon tank is acceptable.  

How Many Angelfish In A 75-Gallon Tank? 

The ideal number of angelfish for a 75-gallon tank is 6. Angelfish are schooling fish. So, 6 would be the perfect number to form a school! Angelfish grow pretty big and get aggressive as they get older. Therefore, you shouldn’t overstock them!  

Now, let’s look at the rule/formula that I mentioned above. 

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Dick Mill’s Golden Formula To Calculate Stocking Number For Tanks

In his book, You And Your Aquarium, acclaimed aquarist and author Dick Mills shared a simple rule to help hobbyists achieve the correct stocking number for their tanks. 

According to him, we should allocate 12 square inches of open tank surface to an inch of fish for tropical fish. Likewise, 30 square inches per inch for cold freshwater fish like goldfish. And lastly, 48 square inches per inch of tropical marine fish. 

Most experienced fish hobbyists agree the floor and surface area of the tank calculation to be the best for stocking fish. 

The floor and surface area of the aquarium denotes how much floor space and water surface there is, respectively. Therefore, you will only need to measure how wide and long the tank is. No need to take height into account. 

Let’s look at the formula and a few examples now. This should make things clear! 

Step 1: 

Find out the tank’s surface area by multiplying its length and width. You don’t need to measure the height. 

Surface area = (L x W)

Step 2: 

In the second step, you can calculate how many inches of angelfish your tank can hold by dividing the surface area by the number 12. 

That’s because mid-range tropical fish like angelfish require 12 square inches of area per inch. 

Total inches of angelfish the tank can hold = Surface area / 12 

Step 3: 

Finally, find out how many angelfish the tank can hold by dividing the above answer by 12, which is the average height of an adult angelfish. 

Total number of angelfish the tank can hold = Total inches of angelfish / 12

Using this formula, let’s calculate how many angelfish in a 75-gallon tank is alright. 

A 75-gallon fish tank has the following dimensions: 48″ x 18″ x 21″ (L x W x H)

First, let’s calculate the surface area. 

Total surface area = L x W 

                                  = 48 x 18 

                                  = 864 square inches 


Total inches of angelfish the tank can hold = 864 / 12  = 72


Total number of angelfish the tank can hold = 72/12 = 6

So, there you go! 

I’ll calculate the stocking numbers for a few more aquarium sizes using this same formula. I hope this is going to be helpful. 

The calculation is done based on the surface area:

300 square inches 2 angelfish
450 square inches 3 angelfish
600 square inches 4 angelfish
800 square inches 5 to 6 angelfish
1000 square inches 6 to 7 angelfish 
1200 square inches 8 to 9 angelfish
1500 square inches 10 to 11 angelfish 

Why Does The One Inch Per Gallon Rule Doesn’t Work? 

Credits: Jenly (Creative Commons license)

One inch per gallon is the hard and fast rule practiced quite exuberantly in the hobby. However, this technique has a lot of drawbacks. At best, it is only suitable for small fish like guppies and tetra. 

The rule itself is pretty simple. 

For every gallon of the water the tank holds, you can add a 1-inch fish using the fish’s length as a measurement. 

However, the biggest disadvantage of this rule is that it doesn’t consider the height of the fish. Likewise, the space the decors and plants take up is also ignored. 

Naturally, any aquarium plants, decorations, and gravel you add will take away the number of gallons the tank can actually hold. 

The amount of waste produced, the fish’s activity levels, and schooling behavior are also disregarded. 

Imagine adding a 10-inch oscar in a 10-gallon tank. Or 2 10-inch catfish in a 20-gallon tank! 

How Many Angelfish In A 75-Gallon Tank? Public Poll! 

Note: The opinions expressed purely belong to the respective hobbyists! 

“I naturally scoured through at least a dozen different forums to look for answers shared by real hobbyists like you and me. And the answers I found were pretty interesting!” 

“For a 75-gallon tank, I would add 5-7 angels. Maybe more, but I generally stick to the 10 gallons per fish rule for a group of 4 or more!”

“I would put no more than 6 angelfish in a 75-gallon tank. Since these fish show aggressiveness, I would put in some other fish with the same temperament but won’t bite off their long fins.”

“I agree that 5-6 angelfish would be the limit in a 75-gallon tank, assuming that it’s a 4-foot tank. Since this is a shoaling species, having fewer than 5 will inevitably lead to bullying.”

“I had a different experience with 5 adult angels in a planted 75-gallon tank. 2 paired up, and the rest of the 3 were forced into maybe 18 inches of the tank space!”

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Ideal Tank Shape For Angelfish

Angelfish need tall aquariums to accommodate their body shape due to their tall stature. 

Also, here’s a bit of information on tank shapes and their significance that can help you make a better decision. 

Good bacteria process the fish waste at the tank’s base. On the other hand, oxygen exchange happens at the tank’s surface.

So, wider floor space allows your tank’s nitrogen cycle to process more fish waste. And a larger top surface area enables more oxygen cycling. 

Therefore, a longer, low tank has a greater carrying capacity than a shorter, taller one that holds the same amount of water. ‘

But since angelfish need taller tanks, you need to stay on top of the water parameters to ensure that the water is well aerated and the waste is being processed efficiently. 

4 Things You Should Know Before Stocking Angelfish 

Before deciding on the stocking number or the ideal tank size for your fish, you need to go through some basics. There are certain factors you shouldn’t miss to take into account. For instance, angelfish live a long life and can grow pretty big. Also, they have a mean temper! 

Angelfish live a long life. 

If you offer the proper care and diet, angelfish can live up to 10 years in captivity. That’s almost as long as dogs! So, you shouldn’t forget to take the fish’s long lifespan into account. 

These fish are a long-term commitment. Therefore, you need to make decisions that allow you to take good care of them throughout their life, even if it means cutting down the stocking numbers or investing in a big tank. 

Angelfish can grow quite big. 

In nature, angelfish are known to grow as big as dinner plates! Luckily, in tanks, they plateau at around 6-8 inches. Nonetheless, 6-8 inches is still pretty big for a captive fish. 

The bigger the fish, the greater the bioload produced and the need for the swimming area.

Therefore, the fish’s size is an indispensable parameter to consider. 

Angelfish have a mean temper. 

At the end of the day, angelfish are cichlids. And like most cichlids, they are hardwired by nature to be aggressive, short-tempered, and territorial. 

When the angelfish are young, you can get away with overstocking them. But once they come of age, they won’t mind fighting to the death over territory and resources. 

Therefore, it’s critical to ensure that each angelfish has ample space to carve its tiny territory. 

Small tanks are harder to look after. 

As beginners, we often assume that smaller tanks are easy to maintain. But that’s the farthest from the truth, my friend! The tinier the tank, the slimmer the margin for error is. 

The parameters in small tanks change randomly and abruptly. They’re a lot more volatile than we give them credit for. 

Thus, with small tanks, you’d need to be on your toes all the time to care for them. 

Final Words: How Many Angelfish In A 75-Gallon Tank

I strongly recommend not adding more than 6 angelfish in a 75-gallon tank. I have kept just 3 mated pairs in a similarly sized tank. 

I follow the easy rule given by acclaimed aquarist Dick Mills who states that for tropical fish like angelfish, we should allocate a minimum of 12 square inches of surface area per inch of your fish. 

The one gallon per inch of the fish doesn’t apply for mid-sized species like angelfish. So, don’t fall for that! 

And lastly, don’t forget to consider angelfish’s long lifespan, maximum potential size, and bad temper when finalizing the stocking number or ideal tank size. 

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