How Many Fish Can Live In a 75 Gallon Tank?

Stocking your aquarium with the appropriate number of fish is crucial for their health. A 75-gallon tank is tantalizingly large and offers many possibilities for marine and freshwater fish species. It is a common mistake for aquarists to get carried away and overstock their tanks.

A 75-gallon tank can hold 25-30 fish, depending on their size and species. The guideline for stocking is 1 inch of adult fish size per gallon of water in the tank. When applying this rule, keep in mind a 75 gallon tank only holds about 70 gallons of water.

There is no one-size-fits-all rule for how many fish you can keep in a particular fish tank. The ideal stocking rate depends on various factors – the species of fish, their behavior, whether they school, the shape of the tank, and the filtration of the water. This article discusses how many fish can be kept in a 75-gallon tank and which species can live together.  

Fish That Can Be Kept in a 75-Gallon Aquarium

Tinfoil Barbs | Source: Deposit Photos

Here are some freshwater species can live in a 75-gallon tank:

SpeciesHow Many?
Fancy Goldfish4
German Blue Ram6 (3 Pairs)
Silver Dollars5-7
Weather Loaches8-10
Zebra Danios40-50
Bristlenose Plecos1-2
Harlequin Rasbora50-60
Neon Tetras50
Tinfoil Barbs1
Sailfin Mollies9
saddleback clownfish | Source: Deposit Photos

Here are some marine species can be kept in a 75-gallon tank:

SpeciesHow Many?
Banggai Cardinalfish1
Clownfish1-2
Mandarin Fish1
Yellow Tang1
Royal Gramma6

Overcrowding: The Most Common Problem in 75-Gallon Tanks

When people upgrade from a smaller tank to a 75-gallon tank, they overestimate how many fish they can keep in the new tank. One must carefully consider the characteristics of individual fish species you keep together in a 75-gallon tank. 

Larger-bodies species obviously need more space than smaller fish. Some fish, like bettas and cichlids, are territorial and aggressive, needing greater tank space relative to their size. The fish you choose to keep together should not be a threat to one another. 

Overstocking a tank puts all the fish at risk and threatens the health of the aquarium. It causes decreased water quality, fish stress, bully each other, their growth is stunted, and they succumb to diseases

lake Malawi cichlids | Source: Deposit Photos

If a tank is overstocked, the fish produce more waste than the filtration system can handle, so excess waste remains in the water, causing algal blooms and higher levels of nitrates and ammonia in the water. This causes them to gasp

Filtration Affects How Many Fish You Can Keep

Fish produce waste, and to prevent ammonia, dirt, and debris from building up in the tank, you use a filtration system. 

The filtration of the water in the aquarium is a key factor that determines the number of fish you can keep in a 75-gallon tank. If the aquarium water is sufficiently filtered, the tank can accommodate a greater number of fish.

A sound filtration system that is appropriate for the size of the tank and the number of fish is essential for a healthy tank. It filters out particles of debris and prevents the build up of biological toxins in the water. 

An aquarium filter needs to circulate 4 times the water volume in the tank each hour. Therefore, a 75-gallon tank requires a filter with a flow rate of over 300 gallons per hour

Calculate The Ideal Stocking Rate for a 75-Gallon Tank

There are various methods to calculate how many fish can be kept in an aquarium of a given size. It is wise to take a combined approach and consider the following factors:

  • The body shape and behavioral characteristics of the fish species you want to keep. For example, Cichlids are territorial, and each fish needs their own space in a tank. 
  • Certain fish species survive best when they have enough of their kind in the tank to school. These fish must be kept in groups, not singly or as pairs. 
  • When we buy fish, they are often juveniles that still have a lot of growing to do. Work with a fishes’ adult size when calculating the stocking rate.
  • Are there live or artificial plants in the tank?
  • The volume of water in the tank is usually 10-15% less than the total tank volume, as the tank is also filled with rocks, sand, gravel, and plants.

The One-Inch-Per-Gallon Rule

The most common way to get a rough estimate of how many fish can be kept in a tank is the one-inch-per-gallon rule. Keep one inch of adult-size fish for every gallon of water in the tank

This rule gives only an approximation, and one must still consider the above factors. Larger bodied fish, like goldfish and cichlids, need more space than this. It is better to be generous and work on one inch of fish for every two gallons of water in the tank.

The Surface Area Rule

At the surface, there is an oxygen exchange between the air and water. The greater the surface area of the water in the tank, the more oxygen is exchanged, the more fish can be kept in the tank. Thus, a tall, slender tank with the same volume as a wider, shorter tank can accommodate fewer fish

According to the surface area rule, a healthy stocking rate is one inch of adult-size fish for every 20 square inches of tank water surface area. This rule helps in estimating the stock capacity for unusually shaped tanks. 

Stocking Ideas for a 75-Gallon Tank

Consider the following stocking ideas for your 75-gallon tank:

  • 6 Giant Danios or Bueno Aires tetras, 3 Tinfoil Barbs, 7 or 8 Cory’s and an apple snail
  • 2 German Blue Ram, 2 freshwater angelfish, 4 Honey, 12 Bronze or Serbal Cory, 12 Rummy Nose Tetra, and 1 Britlenose Pleco
  • 1 pearl Gourami, 1 fire mouth Meeki, 1 Siamese algae eater, 3 Serapi tetra, 4 Cinnamon Loaches, 10 Zebra Danio, 10 Cherry Barbs, and 10 Cories.
  • A community tank with 2 freshwater Angelfish, 1 or 2 Marbled Hatchetfish, 6 Zebra Danios, and 4 Kuhli Loaches.
  • A vivid species tank starring 4 or 5 Electric Blue Acaras. 

Conclusion

There are a wide variety of marine and freshwater communities that can live in a 75-gallon tank. A 75-gallon tank can generally hold around 25 to 30 fish, but the number depends on factors such as:

  • The size, shape, and behavioral characteristics of the fish.
  • The tanks filtration system.
  • The surface area of the water in the tank.
  • Whether there is real or artificial vegetation in the tank. 

Overstocking an aquarium is a terrible mistake that threatens the health of all the fish in the tank. Overstocking makes tanks more difficult to manage, as the fish produce more waste than the filtration system can handle.