What Fish to Buy for a Small Aquarium-Our Opinion

You may live in a tiny studio apartment or be the parent of a child who wants to give their first pet a go. Either way, you have found yourself wanting fish, but lack the room to put a large aquarium in your personal spaces. A small aquarium is what you need, but it needs fish too.

What fish to buy for a small aquarium? For a small aquarium, you want to fill it with fish breeds that are small and will not grow too much over time. If you add fish that are too large, you risk overcrowding the tank which can result in poor living conditions for the fish like too much waste for the size of the tank.

It is no problem at all to have a small aquarium, just be sure the size of your fish coincides with the size of your tank. Continue reading to find the best fish for your tiny tank, how small of a tank is too small, and the negative effects a small tank can have on your fish.

The Best Fish for Your Tiny Tank

There truly are thousands of different options when it comes to the fish available for your home aquarium, but when you want to scale down a bit on the size, your options become a bit more limited. Have no fear though, there are still plenty of fish available to suit your tastes. The biggest concern is purchasing a fish that will not grow much over time.

Let’s get to talking about five of the best fish for your little tank and what makes them great house dwellers. The best fish for a small aquarium are:

  1. Betta Splendens
  2. Fancy Guppy 
  3. Neon Tetras 
  4. Rasboras 
  5. Corydoras 

Betta Splendens

Betta Splendens fall at the top because these fish are both beautiful and do just fine in a small space. What is so great about these little guys is they come in practically every color imaginable. Do you want to match your fish to your perfect blue suede couch, do you want it to stand flush with your bright green curtains? A beta fish can be all that for you and more. After all, who doesn’t want their fish to match their house decor? 

There are a few things to consider with this beauty though. First, male betta fish are typically very territorial. For your tank, this means if you purchase a male, be sure to only put one within your aquarium. 

If you were to put two or more, you risk the chance of one attacking the other to the point of death. These guys do not mess around when it comes to their space, so be sure to adhere to this if you find yourself coming home with a boy. One is better than none. 

Also, betta fish require a special sort of care. There is nothing particularly taxing to this care, simply rules to adhere to. Betta fish do best in warmer water, so be sure to keep them in water that is around 75 and 80 degrees. 

To keep this temperature, place the aquarium in an area that doesn’t fluctuate much in its conditions. Bettas also need to be carefully extracted when their tanks are being cleaned as their fins are very fragile and can tear with one wrong move.

Fancy Guppies

Fancy guppies are as fun as their name sounds. These little guys are curious, fun-loving, and great little friends to their own kind and other tank mates. Just like betta fish, fancy guppies come in a variety of different colors. 

Even more, they have a nice shine to them that glints, and they dart from side to side of their little aquarium home. They also like warmer water, so be sure to keep them in an area that can give this to them.

Even though these fish do well in a crowd, be sure to try and keep the numbers below ten for a small tank to avoid overcrowding. If you get too many in a small tank it can lead to too much waste which can result in a very dirty aquarium in very little time. 

Conditions for these fish are important as they are rather particular about their environment. Fancy Guppies want things spic and span, otherwise, they begin to get a bit antsy.

 Neon Tetras

Neon tetras are as cute as they come. Their blue bodies with flashes of red on their bellies are fun little visuals to watch and they dart to and fro. Similar to fancy guppies, neon tetras do very well in groups. 

If you are someone who does not want only one fish but also has no desire to figure out which fish go along well with others, neon tetras are a great option to stock up your tank. Keep in mind not to overcrowd as well with these little guys too.

Neon tetras are more particular than most fish about their water conditions. They want their water to be absolutely pristine. This may be a pain if you are someone who struggles to keep up with regular water changes, but be sure to keep this at the top of your priority list when it comes to this fish.

If they are in dirty water, their healthy scales can get rather brittle and their overall health can decline. If this happens, you may end up with fish belly-up one morning. 


Rasboras are wonderful because they only grow to be about two inches long. For those of you installing a small aquarium, this is the kind of news you need! Even better, they are so fun to look at. 

Harlequin and lambchop rasboras are bright orange with a black triangle right on the back of them. They do just fine in groups of about six and will not cause a big fuss if added in with other fish. They are the peacekeepers among fish- friends, not foes.

When adding new fish, you want your little water bugs to get along. If you put in breeds that are aggressive, tend to hoard food, or even some that simply do not do well living with others due to their need for a bit of personal space, you could end up with fish that turn on one another leaving you desperate to solve your fish problems before one loses a life. 



Last on our list of small tank friendly fish, we have corydoras. Corydoras are somewhat iconic as nearly 160 different species have been found. These fish have a very unique look to them as their mouths look like that of a teeny tiny catfish. 

Even better, these fish are super playful when it comes to their own kind. They are social butterflies, so to speak, and need playmates of the same species to keep them happy and healthy.

One factor to consider when getting these fish is that they are bottom dwellers. If you want the type of fish that is going to swim all about the tank from top to bottom, these are not your best bet. They like the bottom and they will not stray too far from it. 

For this reason, they will need a special sort of sinking food as they will not make their way to the top to feed. There are plenty of options out there, just be sure too much build-up does not occur at the bottom. 

How Small of an Aquarium is too Small for Your Fish? 

There are all sorts of options for small fish tanks out there. Some you will find in the typical rectangular shape, others have all sorts of nooks and crannies in shapes that look more like art than they do a fish home, and there are even some you can mount on your wall. 

Although the variety is super interesting, there comes a point when your fish tank loses its functionality and becomes too small for your fish to live comfortably. There are many different variables that come into play when you seek to find out how small is too small for the size of your fish tank.

You have to consider the size of your fish, how big it will grow if purchased as a juvenile, the amount of space it needs naturally, and how many fish you plan to have contained in the same tank. Once you have taken all of these points into consideration, you can determine how big of a tank you need to keep your fish well. 

There needs to be enough room for your fish to be able to swim comfortably without it being a constant circle. You also want to ensure that at the very least, your fish will not make up a large part of the tank itself.

Although it may look like a neat statement in your home decor, it is unwise to put a fish in a very small area like a vase or a very small wall bowl. Your fish need space to roam and if they are too cramped, they will likely suffer. 

If you have a very small fish that does not need 10 gallons worth of room, it would be completely appropriate to fit them in something that is small like a 5-gallon tank or even a decent-sized bowl. Think of yourself and the space that you would need to not feel encroached upon or overcrowded. Although fish are little creatures, they need the same consideration when it comes to their living space. 

The Effects of Aquariums that are Too Small

 No matter how cute or tempting small aquariums may be, putting your fish into an area that is entirely too small can result in a poor ecosystem within the tank, crowded environments for multiple fish, constantly dirty water, and potential fish death.

Consider the following effects of using an aquarium that is too small:

Unnatural Death

 Earlier I noted the fact that you need to make sure that your fish will not get too big over time. If you buy a juvenile fish, they still have time to grow and will do so whether it be a small growth or they triple in size. 

This is an important thing to consider because if you have your fish in too small of an area, it affects how they grow. Think of it like when you were in middle school and you put on pants that were from last season. The hem was too short and the button at the waste was hanging on for dear life as it nearly ripped from the seam. 

After this experience, you knew there was no way you could fit into those pants any longer and even if you did squeeze into them for one more day, you would be completely and utterly uncomfortable. 

This same situation can be applied to a fish and an aquarium that is too small. Once they begin to grow, they need room to properly grow into the body they were designed to have. Without ample space, a fish’s growth can be stunted, their spines can deform, and muscles can atrophy due to their inability to move adequately.

Because of all of these physical implications on a fish, it can lead to a very rapid and unnecessary death. You want your fish to have a long, good life in its little water haven. If you choose to disregard its spatial needs, it will very become a fish you once loved. Take heed to their needs and give them enough space to roam. If you cannot supply this, it is best to stick with window shopping for fish.

Competition for Room

If you ever shared a college dorm, you know what it feels like to constantly be up close and personal with someone else’s space. You share the same room that is barely big enough for one person, none the less two, you eat meals less than 15 feet apart, your dressers are back to back, and you know every single good and annoying habit they possess. 

When you got out of that dorm, you were free at last and instantly in a better headspace. If you have a tank that holds more than one fish, then you have the responsibility to give every little guy in your tank enough space to where they are not constantly bumping into one another.

Many times people will argue this point because they like their fish to be denser as it is prettier to look at, however, your fish do not share in this same sentiment. Sooner rather than later, tensions will start to rise and your fish will become quick enemies. 

Because of the lack of space, fish will begin to compete for the room itself which typically results in a fish fight. It can also cause your fish to take on aggressive behaviors that are not typical for that particular breed. Give your fish enough space to hide in various areas and getaway every now and again. After all, who doesn’t need a little alone time from time to time?

Poor Water Conditions  

Fish are not just little bodies that swim. They produce waste- and a lot of it. This is a critical point to consider, especially when you are talking about the science of their water. Fish waste creates ammonia and bacteria present within the aquarium converts that ammonia to nitrate. 

When this happens, a less-toxic nitrate is produced which means a complete cycle has happened for your aquarium. When you have a small aquarium, bacteria can explode due to excess waste in a small area, which can create nasty water conditions for your fish. 

You must also be vigilant in completing partial water changes for your aquarium to make sure that bacteria do not run amuck. If you do not replace the water, an excess build-up of bacteria and debris will cause your fish to be in a habitat that is unsustainable for their little lives. 

When you are considering water conditions, be sure to keep in mind the appropriate amount of feeding that your fish need. Many times, fish owners tend to overfeed their water babies and because of this, it leads to excess food settled at the bottom of the tank. This contributes to poor water conditions because excess food means a food source for bad bacteria to feed on. Keep it clean and your water (and fish) will be sitting pretty. 


So, if you are looking for what fish to buy for a small aquarium, be sure to consider the needs of the fish and the dimensions of the tank. Choose fish that will get along well socially and maintain their own space. Betta Splendens, Fancy Guppies, Neon Tetras, Rasboras, or Corydoras are great for small aquariums. Then, be sure to take care of the aquarium and avoid adding too many fish or using too small of an aquarium for the number of fish that you have. 


I'm passionate about fish pets and love sharing everything I learn about them.

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