Fish tank too small (3 things to do)

After reading this article “Fish Tank too small” the reader will be able to know about the effects of a fish tank too small for fish and what are the factors you should consider while selecting a fish tank. 

Fish tank too small for fish

If you have ever heard of the fish that is growing as big as its enclosure then it is not a good thing. If your fish grows in a fish tank too small for him he will experience stunted growth, spinal deformities and other health problems. 

Effects of too-small fish tank

Following are the effects of too small fish tank for fish:

Fighting for survival

Imagine you are living in a room with a person. Initially, there is fun having a roommate but as the things go on it will start to grate on your nerves. 

You want this man out of your territory. This though will haunt your mind and the fight for territory will start. 

It is quite similar for your fish too. When you have a fish tank too small for your betta fish (tropical fish) in a betta tank. The other member of the fish will soon be kicked out from the freshwater fish in the freshwater aquarium. 

The fight for food and shelter will start among the fishes of the betta tank. This will create a mess in your nano aquarium. 

To avoid this you need to have a large tank. If you cannot afford a large tank at the moment, then you need to monitor the behaviour of the fishes in the tank to avoid unnecessary mess. Proper aeration is required by the filters. 

In a large fish tank, there are plenty of hiding places for the fishes to avoid other fishes and this keeps the environment friendly and safe for the growth of all the fishes. 

You need to provide high-quality food to your betta fish in a betta fish bowl. 

Shortened life span

The one problem of fish tanks being too small is the shortened life span of the fish. 

The fish in a too-small fish tank experience stunted growth due to shortened nutrient supply. Malnutrition leads to stunted growth. 

Stress and illness 

Think about your home and your room. If you are locked up in a single room then soon you will get stressed up. Same is the case with the fish. 

Rivers and lakes are the natural environments of the fish. Think about a fish that is in a 20-gallon fish tank and a fish that is in a cup in a pet store. The former will enjoy his life and spread his fins and do more and more exercise. On the other hand, the fish in a cup will soon be stressed up and fall ill. 

A happy fish remain healthy and fit and remain disease-free because his immune system is active to fight the disease. 

The stressed fish has a depressed immune system and falls ill very quickly. Signs of stressed up fish are neurological signs, parasitic and fungal infections and gulping air at the surface of the water to get extra oxygen. 

Water quality

The nitrogen cycle is the key to keep the water safe and healthy for your fish. 

The waste released by the fish is converted to ammonia and is processed by bacteria to convert it into less toxic substances. 

If the fish tank is too small for your fish and there is no filtration system or no changing of water then the waste will build up affecting the quality of the water in the fish tank. Poor quality of water can cause the death of the fish in your aquarium. 

Water temperature fluctuations

Temperature fluctuations are the biggest problems you will be facing while setting up a fish tank too small for your fish.

The smaller fish tanks are subjected to more temperature fluctuations then another tank. This is because the smaller tanks can absorb heat from the light inside the tank or can be affected by just sitting near the window of the room.

The larger tanks are not subjected to temperature change that’s why you should need to think about your larger aquarium.

The temperature can give your fish a cold shock if the temperature falls below the normal level of the fish tank. It can also be harmful if the temperature rises beyond the limit of the fish tank.

What should you do if your fish tank is too small?

First, you need to become a doctor of your fish. This means that you need to treat the stressed fishes or the fishes that fall ill due to the poor quality of the water. You may need to make a small hospital in the tank or you may need to treat your fish away from the other fishes of the small gallon tank.

The second thing you can do is to give away your healthy fish in the market or to somebody in your neighbourhood. I know it is hard to do it because you love your healthy fish and it is difficult to let it go. But you need to understand that it is for your healthy fish. Most pet stores are willing to take your healthy fish if you are not willing to buy a new one.

If you are expecting the store to pay you then you might give it a second thought if you have past the refund period. It is because the owner of the pet store has fed your fish and gave your fish a space in the tank which cost him some money.

If you are willing to keep all of your fish to yourself then you need to make space for them. You either need to buy a second tank or a larger tank for your fish. If you buy a second fish tank then you need to make sure that the size of the fish tank is large enough to accompany the fishes of other tanks.

Next, we will teach you how to select your fish tank for your fish.

How to choose the right size tank for your fish?

If you are willing to keep a fish then you need to buy the right size tank for your fish. You surely do not want to buy a fish tank that is too small for your fish.

Here is the list of the factors you need to consider to buy your right size tank:

  • Size of the fish
  • Number of fish
  • Whether the fish is community fish or a solo fish
  • Territorial or non-territorial fish
  • How heavily the fish tank is planted or decorated 
  • The space needed by the fish

Size of the fish

You should buy the adult size of the fish because you need it to not grow further and you have the right size of the fish to monitor.

For slim bodied fishes like that of guppies, the role of the thumb is 1 gallon of water per inch of the fish. So if you have a guppy fish of 2 inches you need 2 gallons of water as per the thumb rule of the fish tank.

For large-bodied fishes like fancy goldfish or angelfish, you need 2 gallons of water per inch of the fish. If you have a goldfish of 2 inches then you will be needing a water tank having 4 gallons of the water. 

Similarly, if you have a fish of 6 inches then you will be needing water of 12 gallons in your fish tank. Oranda goldfish requires 20 Gallon of the fish tank. 

Territorial/shy fish

If you are dealing with territorial fishes ( semi-aggressive or aggressive) then you will need to provide separate territories for your territorial fishes. 

Similarly, if you are dealing with shy fishes then you will need to provide enough hiding places for the shy fishes to hide from other fishes.


Some fishes like to swim and are swimmers. They need extra space to swim and enjoy their swimming activity. You need to make sure that the fish you have is a swimmer or a non-swimmer. This information is available at the pet store.

Planted/decorated aquarium

If you have a heavily planted tank then you need to think about getting fewer fishes in your tank. Heavily planted or decorated tank means you have less space to provide to your fish. Also, you need to know about the behaviour of the fish you are dealing with. 

You need a fish that does not require much space in your heavily planted aquarium. If you put a fish that is a free swimmer then your fish will be stressed and you will not be able to meet his needs.


In this article “Fish tank too small” we have discussed the adverse effect of fish tanks being too small for fish and the factors on which the choice of your fish tank depends. 

Feel free to ask anything about “Fish tank too small” in the comment section below. 

FAQ; Fish tank too small

Frequently asked questions of “Fishtank too small” are:

What is the smallest size fish tank?

The smallest size fish tank should be 10 gallons. If you are planning to have a single fish in the tank then the 10-gallon tank is the best. But if you are planning to have schooling fish then you will be needing an even larger tank. 

Is it cruel to keep fish in a small tank?

Yes, if the fish tank is too small for your fish and the equipment in it. If your fish doesn’t get a good quality of water and does not have the space to spread its fins then it is cruel. 

How do I increase the size of my fish tank?

Following are the things you can do to increase the fish tank size:

  • Provide your fish with a larger tank
  • Allow the fish to adjust to his new environment 
  • Always keep the water clean
  • Provide high-quality water
  • Maintain the appropriate temperature
  • Provide high-quality food

Is it true a shark won’t grow in a fish tank?

No, they won’t grow to the size of the tank. They will either outgrow or won’t even grow to the full size of the tank. The rule of thumb is one gallon per inch of fully grown fish. 

Can a shark live in a fish tank?

No, all shark species do not grow in the fish tank. They will only grow in the saltwater aquarium but only a few species grow in saltwater aquariums. Not all the species of shares sold by the pet stores are good to be kept as a pet. 

What happens if you put a baby shark in a fish tank?

It will quickly outgrow the fish tank. The growth of shark in the fish tank depends upon the species of shark. If you have a shark like that of Dwarf lanternshark then it wouldn’t grow as big as the size of the fish tank. 


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