What Happens If A Fish Tank Is Too Small?

A popular question often asked is “what happens if a fish tank is too small?”. This is usually asked by newbie fish keepers, as they generally start off with small fish tanks as they feel larger tanks are more intimidating.

Here are just a few potential problems of having a fish tank that is too small:

  • Stunted Growth
  • Reduced Lifespan
  • Reduced Water Quality
  • Stress And Illness

We will cover all of these, plus much more inside of this post as well giving you the best advice on what size tank you actually need.

What Happens If You Put A Fish In A Small Tank?

What Happens If You Put A Fish In A Small Tank

Having a fish tank that is too small may not seem like a big deal, but it can actually cause many problems and be detrimental to the health of your fish. It is often said that the bigger the aquarium, the happier your fish will be.

It’s better to have an aquarium that is too big than too small as not many problems can occur. Let’s take a look at problems with having a tank that is too small.

1. Stunted Growth

Your probably familiar with the following statement: “Fish only grow to the size of the tank”. This is completely wrong and is a myth that has come from the owners of goldfish.

Goldfish continue to grow until they die, or what’s known as an indeterminate grower. A goldfish will not continue to grow if you place them inside of a small aquarium.

It’s not the fact that a fish grows to the size of the tank, what actually happens is a fish’s growth is stunted which can be detrimental to the health of your fish as it causes internal organ failure.

2. Reduced Lifespan

Keeping fish in an undersized aquarium can significantly reduce their lifespan. Here are the two main reasons why:

  1. Being cramped in a small space can cause your fish to become stressed. This stress causes their heart to overwork which places a huge amount of tension on it.
  2. As mentioned in above, a small tank will stunt the growth of your fish and can cause internal organ failure because the organs don’t have the space to grow.

3. Aggressive Behavior

So above we mentioned that a fish can become very stressed in a tank that is too small. The stress can cause your fish to become more aggressive towards other fish in the tank. The problem with this is that it is very difficult to turn them back into a friendly fish.

4. Stress And Illness

If you think of how fish live in the wild, they have plenty of space in oceans, rivers, and ponds which allows them to explore their environment. A fish being stuck in a very small space all day can cause stress which can lead to illness.

If you think of yourself and imagine how you would feel being locked away in a tiny room every day, you wouldn’t feel great! Your fish feel exactly the same. A happy and relaxed fish is more capable of fighting off disease and illness.

5. Poor Water Quality

As you can imagine, waste inside of a tiny tank will build up a lot quicker than in a larger one, which cause the quality of the water to quickly go downhill. Unless  frequent partial water changes are made, your fish can become very ill and die.

Not only are you putting your fish in danger, it’s also a lot of hard work and maintenance for yourself. It’s better to just get it right from the start and just invest in a large tank.

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6. Water Temperature Fluctuations

Surprisingly, the temperature of the water can fluctuate much more in a smaller tank than it does in a large one. Keeping the water at a consistent level inside of a small tank can be very difficult.

The reason why this is a problem is because if a fish gets too cold, they can go into temperature shock which can kill them. Being too warm can also have a harmful effect.

7. Fighting for Space

If a number of fish are cramped up inside of a small tank, especially fish who are territorial, can cause fighting. Fish love their own space and their own hiding places so it’s very important to provide this for the health and happiness of your fish.

What Size Fish Tank Should I Get?

The best way to go about this is to first of all decide what kind of fish you want. Most people have specific breeds in mind, but they make the mistake of purchasing the tank first.

It’s better decide on the breeds, and then purchase a tank that is going to be suitable. It’s also a good idea have an idea of the number of fish you wish to keep in the tank.

The Bigger The Better

So after looking at all of the negative things of a tank that is too small, it’s always better to go with a tank that is too big than too small. As well as your fish being happier and healthier, surprisingly, larger tanks are also easier to maintain.

The condition of the water along with the temperature are crucial factors for the health of your fish. It’s a lot easier to maintain these conditions in a larger tank. Inside a large tank, it takes longer for ammonia to spike, which means gives you longer to react.

How To Choose Fish Tank Size

Here’s a quick breakdown of things you need to decide when choosing a tank:

  • Which breed of fish you want
  • How many fish
  • Do the fish need to be grouped
  • Are the fish territorial
  • How many decorations do you want in the tank
  • The amount of swimming space needed

Popular Fish and Their Tank Size Requirements

Species Min Tank Size (individuals) Min Tank Size (school)
Green Chromis 10 Gallons 40 Gallons
Common Clownfish 10 Gallons 60 Gallons
Royal Gramma 30 Gallons 100 Gallons
Oscar 60 Gallons 150 Gallons
Neon Tetra 5 Gallons 15 Gallons
Guppies 5 Gallons 20 Gallons

Commonly Asked Questions

Do fish get bored in small tanks?

Although it’s difficult to figure out if a fish get’s bored in the same way as a human does, the nature of a tank does have an influence on a fish’s brain and behavior. This means if an aquarium has no decorations, plants, rocks, or is too small, a fish will be unhappy.

Can fish die if the tank is too small?

Fish can certainly die if a tank is too small due to the following reasons:

Stunted growth: The growth of a fish can become stunted causing internal organs to fail.
Poor water quality: The quality of water can decline very quickly inside of a small tank, and if left untreated can cause disease and illness.
Fighting: With not enough space or hiding places, a small tank can cause fish to fight for territory which can result in them killing each other.


Just to summarize the question of “what happens if a fish tank is too small?”. Always go for a tank that is too big rather than too small. A tank that is too small can be detrimental to the health of your fish.

Before you even pick a tank, first of all what breeds of fish you wish to keep, as well as how many fish.