Not many fish can live happy and healthy lives in a 2.5-gallon tank. If possible, we recommend giving your fish room to roam in a 5-gallon tank. In the fish-keeping hobby, bigger is usually better when it comes to accommodation for your pets!
However, if you are a nano tank hobbyist or want to purchase a GloFish kit, you can make a 2.5-gallon tank work. Also, a well-maintained tank with 2.5 gallons of water is infinitely better than an unfiltered fish bowl or a vase. If you do decide to keep a tiny tank, you must be prepared to carry out frequent water changes and keep the tank immaculately clean to prevent water quality problems from developing.
Key Takeaways
- Tank Size Matters: A 2.5-gallon tank is often too small for fish to thrive, although certain species can survive; bigger tanks are highly recommended for the health and well-being of your aquatic pets.
- Suitable Candidates for Small Tanks: Snails, shrimp, and certain small fish species like bettas and guppies can be kept in a 2.5-gallon tank, but with caveats regarding space and companionship.
- A Tool, Not a Home: Beyond housing a few select creatures, a 2.5-gallon tank is best used for specific purposes such as growing aquatic plants, breeding, as a quarantine tank, or cultivating live food for other fish.
Summary Table
| Fish Species | Tank Size | Remarks |
|---|---|---|
| Betta Fish | 2.5-gallon | Prefer larger tanks; never house males together; too small for female sororities and breeding pairs. |
| Baby Fish (Fry) | 2.5-gallon | Can be used as a nursery for eggs and fry; allows close monitoring. |
| Guppies | 2.5-gallon | Accommodates 1-3; hardy but social, prefers larger groups and tanks. |
| Minnows (Certain Types) | 2.5-gallon | Better than being feeder fish; needs to be in schools which may overcrowd a small tank. |
| Tetras (Various Types) | 2.5-gallon | Can only house one or two; GloFish® tetras kits available for small tanks. |
| Barbs (Small Varieties) | 2.5-gallon | Require a group to form a hierarchy; five or more barbs in this size tank is not recommended. |
| Snails and Shrimp | 2.5-gallon | Thrive in small tanks; snails can reproduce quickly; up to 10 shrimp may be possible. |
| Live Aquatic Plants | 2.5-gallon | Ideal for creating underwater gardens; suitable for later addition of small creatures. |
| Nano Tank Species | 2.5-gallon | Advanced aquarists only; includes Chili rasbora, Galaxy danio, Dwarf cichlids, Killifish, Pygmy corydoras. |
What Fish Can Survive in a 2-Gallon Tank?
Some small fish can survive in a 2-gallon tank, but no fish can thrive in a tank this small, largely because of water quality issues.
I always recommend keeping snails or shrimp if you have a really small tank, and there’s a whole section on them included in this guide to help you get started.
However, if you must keep a fish in a 2-gallon tank, keep reading our list to see what species might work.
Betta Fish
When most people think of fish that do well in a small tank, their minds immediately go to betta fish.
Is a 2.5-Gallon Tank Okay for a Betta?
Yes and no. Your betta will survive, but it’s not an ideal environment for your fish. While your betta would prefer a 5-gallon tank, it can get by with a 2.5-gallon tank and some live plants.
The most important to know is that you must never keep more than one male betta in any tank. These fish are not called Siamese Fighting fish for nothing, and two males together will almost certainly end in carnage.
Unfortunately, a 2.5-gallon tank simply isn’t big enough for a mating pair or a sorority of female bettas.
As Reddit contributor, CootaCoo suggests:
… 2.5 gallons is okay for a retirement tank for a betta (i.e., an old slow betta that can’t / doesn’t swim around very much anymore), but I wouldn’t put one in there for its full lifespan.
So, if you can, please invest in a bigger tank for your betta buddy!
Baby Fish
If you are breeding fish, a 2.5-gallon tank can be perfect for eggs and fry (baby fish).
You can use the small tank to keep eggs safe, and when the fry hatch, you will be able to keep a better eye on them in a smaller tank.
One of the best uses we can think of for a 2.5-gallon tank is a fry tank. Yippee!
Guppies
A 2.5-gallon tank will accommodate one to three guppies. Wild-type guppies are extremely hardy, which is good because 2.5-gallon tanks can be hard to cycle and maintain.
Of course, guppies are schooling fish, so they are better off in a bigger tank with more fishy friends.
Minnows
Many minnows are “feeder fish,” which means they are bred as food for other fish and small reptiles. Although a 2.5-gallon tank is not ideal for most fish, a small tank life for little minnows is better than being another species’ dinner!
I recommend White Cloud Mountain Minnows or Rosy Red Minnows. During my 40 years of fishkeeping experience, I’ve kept many of these cute little guys in tanks of various sizes and shapes, and they’re a real crowd-pleaser. However, you do need to keep these fish in schools of at least six individuals, which can lead to overcrowding in a very small aquarium.
Please don’t keep only one or two minnows. These fish need company and will spend most of their time hiding away if they feel lonely. That leads to stress, which will ultimately kill your minnows.
Tetras
Small tetras are designed for small tanks, but you can only keep one or two in a 2.5-gallon tank. We like the following varieties:
- Cardinal tetras
- Lemon tetras
- Neon tetras
- Harlequin tetras
- Black tetras
- Ember tetras
- Bloodfin tetras
- Black skirt tetras
- Blind cave tetras
- GloFish® tetras
If you are intent on keeping GloFish® tetras, the GloFish® brand sells kits that include everything you need to get started.
For Blind cave tetras, make sure you include a cave in your tank so that the shy fish can hide.
Barbs
Cherry, Checkerboard, and Golden Dwarf barbs are small enough to live in a 2.5-gallon tank. Barbs can be tricky, though. You must keep enough of them to form a hierarchy, which can be a tight squeeze in a small tank.
Some sources say you need at least five barbs to form a functional community, and we really can’t recommend cramming five barbs into a tank this small.
Again, always get a bigger tank if you can!
Can I Put Two Fish in a 2.5-Gallon Tank?
If you must. Some fish, including schooling fish like guppies, will get depressed if they’re kept alone, and as we’ve just discussed, barbs can’t thrive without a five-fish community.
All this being said, a 2.5-gallon tank is never big enough to house multiple species. While it might be tempting to keep a Cherry barb with a Neon tetra, you are setting both fish up for failure.
It would be like housing you with a chimpanzee and no one of your own species to talk to. In other words, it’s just not cool.
If you want to set up a community tank, invest in a bigger tank! If you want your fish to be happy and healthy, invest in a bigger tank!
Okay, okay, you might be asking, “Now, what do I do with this 2.5-gallon tank?” Read on!
Better Than Fish: Snails or Shrimp
Because most fish prefer a larger tank, keeping snails or shrimp is one of the best things you can do with a 2.5-gallon aquarium. Unlike fish, snails will thrive in a small tank and even breed. Careful, though; some types of snails reproduce quickly!
You can also keep five or six Cherry shrimp in a 2.5-gallon tank with no problem at all. Some shrimp keepers have succeeded with up to 10 shrimp in a 2.5-gallon tank!
A teeny tiny aquarium is perfect for a planted shrimp or snail tank, which can include loads of live plants and one or two snails — or plenty of plant life and five or six shrimp!
2.5-Gallon Tanks Are Perfect for Live Aquatic Plants
If you’re not quite ready to keep living creatures in a 2.5-gallon tank, don’t worry! This size tank is perfect for creating a beautiful underwater garden, and you can always add shrimp, snails, or small fish later.
You can also grow moss and algae to feed other fish.
Need Some Bugs?
Another great use for small tanks is growing insect larvae. Your betta might not love living in a 2.5-gallon tank, but it will adore eating mosquito or fruit fly larvae you grow in one.
A 2.5-Gallon Tank Is a Tool
Ultimately, a 2.5-gallon tank is better used as a tool than a permanent home. A small tank can come in handy if you ever need a breeding tank, a quarantine tank, or another temporary home for your fish.
It can also help you grow aquatic plants, interesting live food for your fish, and cute snails and shrimp if you wish.
Nano Tanks Are for Experts Only
One of the reasons 2.5-gallon tanks are not recommended for most fish — and why we keep cautioning you against them — is that small tanks are very hard to cycle.
This means harmful substances, like ammonia, nitrites, and nitrates, can build up quickly, and even trace amounts of ammonia or nitrites can kill your fish.
Advanced nano tank hobbyists can learn to cycle their aquariums and support a wider variety of species, including:
- Chili or mosquito rasbora
- Galaxy danio
- Agassiz’s dwarf cichlid
- Cockatoo dwarf cichlid
- Endler’s livebearer
- Killifish
- Pygmy corydoras
Even in the nano fish-keeping hobby, aquarists swear by shellfish and snails, like the Mexican dwarf crayfish and the Zebra nerite snail.
Please do tons of research before you buy and populate a 2.5-gallon tank, and if you’re looking into nano fish keeping, make sure you have had several successful tanks in larger sizes first.
Also, no matter what fish you choose, please read its care sheet on our site, and do everything you can to keep your fishy friend happy and healthy.
After researching, you might decide to try a community tank instead!
No matter what you choose, our team at Aquariadise wishes you and your new pets the very best of luck!
