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, as well.
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 absolutely have to keep a betta (or another breed) in a small space, a good 2.5-gallon tank can make it work.
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. If you must keep a fish in a 2-gallon tank, keep reading our list to see what species might work.
Better yet, keep snails or shrimp instead (there’s a whole section on this below).
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.
Just make sure you only keep one betta at a time because two males will fight, and a 2.5-gallon tank simply isn’t big enough for a mating pair or a sorority of female bettas.
If you can, please invest in a bigger tank for your betta buddy!
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!
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.
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 is better than being dinner for little minnows.
We recommend White Cloud Mountain Minnows or Rosy Red Minnows. Keep them in schools of six, so they don’t get lonely. Also, beware of overcrowding in such a small tank.
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 the shy fish can hide.
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
- Pygmy corydoras
Remember that most cichlids should be kept by themselves or in male-female pairs in a nano tank, and some species are harder to keep in nano tanks than others.
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!