What Size Fish Tank Should I Get?

A lot of novice aquarists overlook the importance of getting a fish tank that is the correct size.

If you end up getting a fish tank that is too small it can cause lots of problems, think: stunted growth, aggressive fish and unstable water parameters.

Each one of these issues can ultimately lead to your fish dying.

So, in this article we are going to look at what size fish tank you should get before answering whether bigger aquariums are “better”.

What Size Fish Tank Should I Get?

Lots of people get into fishkeeping by first purchasing an aquarium, and then wondering which fish they should get.

This is the wrong way to approach it.

Chances are, you want to start keeping fish because there is a particular breed of fish which you want to keep.

So my advice to you would be to start with the fish.

Sit down and think about the type of fish you want to keep and also how many fish you intend to keep. Once you’ve figured this out, you can work backwards and figure out exactly how big your fish tank should be and also which type of fish tank you should buy (more on that later).

The only time I wouldn’t recommend this is if you’re on a very tight budget.

If you’re on a tight budget and don’t have much spare cash, I would recommend waiting until you can afford to buy and keep the fish that you’d like.

However, if you simply can’t wait, I’d recommend buying the aquarium first and then figuring out how much money you have left to buy your fish with.

Large Public Aquarium
Large public aquarium

Bigger Aquariums are ‘Better’?

As eluded to earlier on, generally speaking the bigger the aquarium the happier your fish will be.

Why is this the case though?

Well as we mentioned earlier on: in small, cramped, environments fish become stressed and aggressive. The opposite happens when fish have lots of space.

Second, larger tanks are far easier to maintain.

As most aquarists will attest to, the biggest problem we generally face is maintaining the water conditions inside the tank; mainly water chemistry and temperature.

Now, the larger the aquarium, the more stable the water is and crucially, the easier it is to keep stable.

Think about it, it takes longer for ammonia to spike in larger tanks so you have more time to react if something goes wrong. As a result a 100 gallon tank is far easier to keep stable than a 30 gallon tank. And again a 30 gallon tank is far easier to keep stable than a nano tank.

This means that the water conditions in a larger tank are more likely to be within healthy tolerances which results in happier fish!

Avoid This Mistake

Small Aquarium
Avoid Small Aquariums

One of the biggest beginner mistakes I see is beginners buying a “starter” tank.

When new aquarists first start, they tend to buy a very small tank, regardless of the species of fish they want.

Although this means that the hobby is affordable and makes it accessible to more people, this is not the ideal way to start. Unfortunately what often happens is people get a small fish tank, such as a 25 gallon tank, and then purchase fish that need more space.

A common example of this is with Oscars.

The thought goes that when the Oscar fish grow from a juvenile to an adult, and needs more space, you can buy a bigger tank for them. In my experience this rarely happens.

People see their Oscar fish surviving in a small tank and think they must be fine, in reality the confinement is hurting them and reducing their life span.

You should always buy the right sized tank from the start. Figure out how much space your fish need (as an adult) and place them in a suitably sized aquarium from the get go.

If you put fish in a small aquarium it can cause lots of problems.

Common Problems with Small Aquariums

There aren’t many problems that occur when you have an aquarium that is too big. In fact as a general rule it’s often said: the bigger the aquarium the happier your fish will be.

However, when you have an aquarium that is too small, it can be devastating for the fish in the tank.

Placing fish in a tank that is too small can cause countless problems, here are the biggest 3 problems it causes:

Nano Coral Reef Aquarium
Nano coral reef aquarium

Issue 1: Stunted Growth

There is a common myth amongst beginner aquarists that:

“Fish only grow to the size of the tank”.

Before I progress let me say here that this is entirely false.

This myth has come from people who keep goldfish. Goldfish are indeterminate growers which means they continue to grow until they die. As you may already know, when placed in a small aquarium goldfish won’t continue to grow. People wrongly assume from this that fish simply grow to the size of the tank. Wrong.

What actually happens is the fish’s growth is stunted and their health has been permanently damaged as a result.

Issue 2: Reduced Lifespan

Not only will placing fish in an undersized aquarium stunt their growth it will also significantly reduce their lifespan.

According to the scientific research, it reduces their lifespan because of two key reasons:

  1. Firstly, in small spaces fish become stressed. This stress places an excessive amount of tension on their heart and causes it to overwork.
  2. Secondly, it causes internal organ failure. As mentioned above, placing fish in a tank which is too small causes stunted growth. This means that the fish’s internal organs don’t have enough space to grow. Ultimately it ends with internal organ failure.
Small Home Aquarium
Small home aquarium

Issues 3: Enhanced Aggression

Finally, the other big problem it can cause is behavioral issues.

There are numerous behavioral implications such as stress, fear and anxiety. But perhaps the biggest issue it can cause is enhanced aggression.

Fish kept in small enclosures can turn aggressive towards the other fish in the tank; this is because they are stressed and scared.

Unfortunately once a fish turns aggressive it is incredibly difficult to turn them back into a friendly communal fish.

The easiest way is to not allow them to become aggressive in the first place!

What’s the Best Sized Aquarium?

If you’ve read everything I’ve wrote in this article so far, you will probably already know that there is no single best sized fish tank.

It can only be answered on a case by case basis. However with that said there are certain rules which you can follow:

  • The larger the aquarium the easier it is to maintain. Think water management and also cleaning.
  • Don’t choose an aquarium which is only just big enough. You should always make sure to get an aquarium larger than needed so your fish flourish.
  • If you can’t provide a suitably sized aquarium, you should choose a different species of fish to keep.
  • The larger the tank, the happier your fish will be.

Where to Put Your Fish Tank?

When considering the size of your aquarium you also need to consider where the fish tank should be placed.

It’s no good having your fish tank in a large open room if the room itself isn’t suitable for a fish tank.

So what makes a room suitable?

  1. Low Light. Your aquarium shouldn’t be placed anywhere where direct daylight can shine onto it. So avoid windows, skylights and this sort of thing.
  2. Low Noise. In a perfect world your aquarium should be placed in a room on its own. However sometimes this isn’t very realistic. Try to put your aquarium away from any noise source (TVs, Kitchen, Radios, Washing Machine etc.).
  3. No Heat. As previously mentioned, maintaining the temperature of your water is one of the most important things you need to do. In order to maintain the water temperature you need to also keep the air temperature around the tank stable. So avoid placing your aquarium near any source of heat.


I hope this article has helped you figure out what size fish tank you should get.

As you will now be aware, there is no perfect one size fits all. You should use this article as your guide and make an informed decision after reading it.

Remember to also research the particular species of fish and find out its individual requirements as well. You can find our species guides here.

Finally, once you’ve got the tank, make sure don’t make these beginner aquarium mistakes.

Leave a comment below letting us know what sized fish tank you’re going to buy…

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