Running a small tank can feel limiting, but the truth is that you can still ensure that you have a thriving community tank even in limited space. It begins with careful selection of the fauna and an understanding of the tank’s limitations. Read on and we’ll introduce you to some great fish fit for miniature tanks.
A Word About 5-Gallon Tanks
If you’re completely new to keeping aquaria it often seems that smaller is better.
That’s not the case.
5-gallon tanks are something that requires a lot more care than most people realize. There are a few factors here but the biggest isn’t the lack of space: it’s the lack of water volume. A 5-gallon tank will often lose 20% or more of the water volume with basic decorations.
For a complete amateur, a tank in the range of 20-40 gallons will be much easier to manage. 10 gallons is the minimum recommended and still requires careful monitoring of the water column to be a success. A test kit is a required investment for anyone running a nano-tank, even if you’re already advanced in the hobby.
That doesn’t mean they’re impossible to manage. You’ll want to do the following if you’re planning on running a 5-gallon tank.
- Cycle the Tank: The tank needs to run without any fish until there is no detectable nitrate or nitrite levels in the water. A single fancy guppy or livebearer can help provide the initial waste load. Still, a good sponge or HOB filter will quickly accumulate bacteria if you just put a pinch of flake in every day.
- Plant the Tank: A nano-tank requires live plants. They can act as a buffer against swinging nitrite levels, keep nitrates down to a minimum, and provide oxygen for the fish that need it. Fast grown plants like Hornwort and Anacharis can be floated and then removed as slower-growing rooted plants take hold.
- Consider Invertebrates: Snails should be placed in any tank that doesn’t contain fish that eat them. Dwarf Amano and Cherry Shrimp are also a good option, but keep the numbers low as their bioload can be noticeable in tanks under 10 gallons.
- Be Mindful of Flow Rate: It’s easy to create a virtual torrent in a 5-gallon tank. While some fish prefer faster flowing water over-filtering can stress fish like Betta and Gourami easily in a small tank.
- Decorate Carefully: Decorations like rocks and driftwood are nice, the latter can even be healthy. They also remove water volume from the total water in the system so stick with plants for the bulk of your decorations.
- Have a Plan… and Stick to It!: Create a full plan for how you intend to stock the tank before you begin setting it up.
One final thing: kits can be great but don’t rely on them. Often the small 5-gallon kits contain inferior equipment. To run a truly successful nano-tank you’ll need to pick each piece of equipment carefully.
1. Betta Splendens
Bettas are one of the best small tank fish that can be found. In addition to being smaller, these fish often exist in stagnant ponds in the wild which removes the need for aeration in the water.
Bettas actually lack gills, instead, they rely on a labyrinth organ which allows them to pull air from the surface of the water. From there, the air passes through this specialized breathing organ and slowly diffuses the oxygen they need through the body.
Bettas have a relatively mild bioload for their size. The addition of some snails and plants can make it easy for them to exist with only the normal level of filtration in their environment. It’s usually advisable to run more than the rated amount of filtration. However, a tank with only a single Betta splendens can run with a mild in-tank filter which reduces the need for a hang-on.
Bettas are easy to care for and intelligent. Unlike many fish, they’ll often watch their owners and come running when they see their food container and some have even been trained which is something generally reserved for highly intelligent species like cichlids.
Bettas are popular for many reasons mainly the lack of specialized care, large variety of color and fin morphs. The ability to exist healthily in small aquaria makes them perfect for nano-tanks. If you’re not familiar with water chemistry or balancing a micro-ecosystem then they’re the best choice for smaller tanks.
2. Dwarf Gourami
Gourami, like Betta, have a labyrinth organ. Many of them grow quite large, the Dwarf Gourami rarely gets over 3 inches in length. This makes them perfect for smaller tanks with some caveats.
If you choose to house a Dwarf Gourami in a 5-gallon aquarium, they should be the only fish contained within. They’re not sloppy eaters but their size puts them at the limit of what can be reasonably handled in a 5-gallon tank.
For your Dwarf Gourami, you’ll also want to plant the tank and make sure that it’s well cycled before you add it. Plants will help with taking care of the additional waste generated by the fish and provide a secure place for them to hide.
A single Amazon sword is a great accompaniment and suitable for beginners. More advanced aquarists may choose to go with a foreground of Anubias and a patch of stemmed plants like Rotala sp. Or Ludwigia sp. to create a garden effect.
3. Pea Puffers
Highly intelligent, rather aggressive, and seriously unique. That’s the pea puffer, which is also known as the dwarf puffer. Be aware, however, that other species such as the figure-8 puffer are sometimes sold under the same trade name.
Pea puffers do well in nano-tanks if you’re able to do a bit of extra work. These fish are carnivorous and a diet of flake isn’t going to provide the nutrients they need. Instead, you’ll need to use bloodworms or snails to provide them with their preferred diet.
It’s advisable to keep bloodworms on hand and to set up a snail breeding vase or fishbowl to keep their diet varied. Do not try to keep them with invertebrates of any sort. Even dwarf shrimp will quickly fall prey to their beaks, instead, just drop some snails in a vase and throw in a chunk of vegetables once in a while. Both Ramshorn and pond snails don’t require any specialized care to form a breeding colony and are ideal food sources.
It’s advisable for someone new to nano-tanks to only keep one of these diminutive puffers in a 5-gallon tank. Two can co-exist in a 5-gallon but you’ll need to have the tank heavily cycled and thoroughly planted. You’ll need to keep an eye on them, pea puffers are individuals and some are more territorial than others.
One last word about these inquisitive little fish: try to find them captive bred. Their introduction to the aquarium trade in the early 2000s has led to a sharp decline in natural populations. Unfortunately, that’s landed them on the IUCN Redlist as a vulnerable species.
4. Scarlet Badis
The Scarlet Badi is a brilliant, crimson fish with a big personality. They’re one of the smallest of the percoid family, which includes perch, and special care must be taken to ensure that they’re happy. While not overly challenging, they’re not the easiest species to raise in a nano-aquarium.
Their small size actually has a high bioload, unfortunately, since they’re primarily carnivores. They will invariably refuse to eat flaked foods and one has to look to their natural diet to find something to replicate.
Live foods are your best bet, although some will accept pellets as they sink through the water. Brine shrimp, small snails, and worms are great and will usually be readily accepted. Ensure you watch them eat, however, as these clever little fish have their own preferences.
Remember that despite their small size Scarlet Badis aren’t schooling fish. The males are highly territorial and even hosting a breeding pair in a 5-gallon tank is really pushing it.
They’re best off as a single display fish in a small tank. To draw the eye you may want to plant the tank well and provide a bit more current than you’d normally find in a small tank. Running a HOB filter set for about 10 gallons will provide the filtration you need.
The enemy of Scarlet Badis is simple: dirty water. Make sure you cycle your tank thoroughly before adding them and keep up with regular water changes. You also need to keep insurance in the form of plants and extra filtration. They have a long lifespan and properly cared for it’s not uncommon for them to last 3 years or more.
5. Sparkling Gourami
The Sparkling Gourami, or Pygmy Gourami depending on who you ask, is another favorite for nano freshwater tanks. They’re actually less than half the maximum size of the Dwarf Gourami. Their iridescent side scales have made them a favorite in both large and small community tanks.
These little gems top out at about 1 ½ inches. In theory, a 5-gallon tank can hold a trio of them once cycled without too much difficulty. On the other hand, the males can be territorial and they’re harder to sex than fish which are truly sexually dimorphic. The only real way to tell is to shine a bright light through them and look for the sexual organs of the female, which requires a lot of anatomical knowledge.
It would be best to only attempt to keep multiple Sparkling Gourami if the tank is well planted and you have a backup plan in case the males begin to clash. Talk to your local fish store or have another tank ready but a good pair or trio can really bring a small tank to life.
Like all nano-fish, you’ll need to heavily plant the aquarium. These gouramis like floating plants and if you want to keep the wattage down you’ll find that Anubias sp. tied to driftwood or rocks and some floating plants like Hornwort or Anacharis make a cozy home for them.
Fortunately, these fish will readily take flake and other commercial fish foods without issue. The occasional bit of bloodworms won’t go amiss but they’re easy to feed and rather hardy fish that will steal the show.
6. Honey Gourami
Honey Gouramis are another great display fish for smaller tanks. They are actually smaller than Dwarf Gourami as well. They come in a golden color but males have a black coloration underneath the lateral line of the fish which gives them an attractive two-tone look.
Still, the Honey Gourami is often around 2.8 inches once fully grown so you should limit your fish choice in a tank as small as 5-gallons to only one of these. They’re still suitable for beginners and their intelligence makes them a charming fish with a lot of personality for their size.
Honey Gourami will readily take the normal flake and pellet foods found in fish stores. For optimal health, a small chunk of frozen bloodworms or brine shrimp make a great way to mix up their diet as well, just don’t get overzealous feeding them or you may end up creating a waste spike in the water column.
Since they have a labyrinth organ you can skip running an air pump although you’ll still want to run adequate filtration. Keep it to a minimum, it’s possible to easily create too much flow for one of these small labyrinth fish if you’re not careful. Instead, use plants to create a bit more control over the number of nitrates in the water.
They do well singly, are easy to keep and make a great alternative to Betta if you’re looking for something unique.
7. Endler’s Livebearers
The closest you’ll get to being able to keep a true school of fish in your 5-gallon tank is by using Endler’s Livebearers. These small fish are closely related to guppies and have vivid color patterns that will catch the eye from across the room, at least in the males.
The striking colors, unfortunately, only belong to the males of the species. The males reach roughly an inch in length when fully grown while the females range from 1.5-2 inches.
Fortunately for those with smaller tanks, it’s actually perfectly fine to keep a male-only setting. With enough plants and a bit of extra filtration, it’s possible to keep 5-7 of them in a 5-gallon tank as long as you’re on top of water changes. They’ll still display frequently but rarely cause damage to each other.
Endler’s Livebearers are some of the easiest fish to keep, hands down. Feed them flake and the occasional chunk of frozen bloodworms and you’ll never have an issue. They’re lively, colorful, and rather calm so you don’t have to worry about fin-nipping or other aggression issues.
Like all smaller fish, you’ll want an abundance of plants. These help them to feel secure and promote brighter coloration.
8. Fancy Guppies
Fancy guppies are one of the most commonly bred aquarium fish and they’re hardy enough to make an excellent option for beginners. The science behind their breeding is extensive, although most people just find the pet store “mutts” to their taste.
Fancy guppies top out at 1.5 inches for males and 2.5 inches for females. Being about 50% larger than Endler’s Livebearers puts them at a disadvantage in smaller tanks. Still, you can safely keep 3-5 guppies in a tank with adequate filtration and weekly water changes.
Guppies are often considered the “default” aquarium fish. They’ll take virtually any commercial food on the market without any real bias. For the most part, these are often enough to keep them healthy over the course of their lives.
Like Endler’s Livebearers, you’ll find that it’s possible to keep an all-male tank if you just want them for decoration. If you do place females in with them try to ensure that you make the majority of the tank female since the males will naturally compete for mating rights.
They’re easy to keep, rather lively, and beautiful fish. This makes them ideal for nano-tanks and the lack of specialized care keeps them easy to keep and breed for even the most amateur of aquarists.
9. Dwarf Rasbora
Dwarf Rasboras are an excellent way to add a splash of red to your tank. They generally hit a bit less than an inch in length as well, so having 3-5 of them is possible in a cycled tank.
They’re spunky fish but extremely peaceful. For those who’d like to keep a snail colony or a few dwarf shrimp as well as their show fish, they’re an excellent option. Just add them gradually to make sure that the filter has adequate bacteria built-up or you may end up in trouble.
They require a bit of extra care. Sudden changes in water conditions have killed many of them in captivity so you’ll need to ensure you keep pH and chemical swings from occurring. For the most part that just means following good aquaria practices but if you’re considering them it’s good to have some experience under your belt. A well-read beginner should do fine as long as they’re careful.
They do well on flake foods, however, so you don’t have to worry about the time and expense of setting up live food for them. Color enhancing flakes with spirulina and carotenoids are desirable to bring their red to the forefront.
Phoenix Rasboras are a closely related species with pretty much the same guidelines for keeping them healthy. They’re slightly smaller but bear a more striking coloration than the dwarf species but the same principles apply.
10. Pygmy Corydoras Catfish
Corydoras catfish are a lively addition and a fast favorite for those who keep peaceful or semi-aggressive community tanks. There are a few small varieties that can fit in a 5-gallon tank but the only one commonly available is the Pygmy Corydoras.
There’s a catch here: Dwarf Corydoras are often mislabeled as Pygmy Cories and vice-versa. They also grow to 1.5”, still small but not quite small enough to keep a school in a 5-gallon aquarium. You can tell them apart by the sides: a Pygmy Cory will have a black lateral line that runs the length of their body. The larger Dwarf Cories will have spots on their back or tail depending on the species.
These lively bottom dwellers are easy to keep, but you should only have 3-5 of them in a 5-gallon tank and no other fish. Invertebrates like dwarf shrimp or snails will be fine to keep alongside them, however.
Corydoras require a sandy substrate. They’ll hurt their mouths and whiskers on gravel or even chunkier planted substrates like standard Flourite. You’ll also need to mix up small algae pellets and bloodworms to provide them with an optimal diet.
That said, Pygmy Corydoras Catfish are a lively group and they provide plenty of entertainment. A heavily planted tank is desirable as well, but make sure that you have an open, sandy area for feeding and allowing them to forage during the day.
Meet their requirements and you’ll have a peaceful, energetic bunch of dwarf catfish to brighten your nano-tank. Requirements aside, they’re still suitable for beginners.
11. Otocinclus Catfish
Otos are a mainstay in planted tanks, especially those where the aquatic garden aspect takes the forefront. They’re extremely small suckerfish. They’re also peaceful enough to keep with other nano-tank inhabitants like dwarf shrimp and snails.
Otos should be kept in groups of at least 3, but 5 is preferable. The problem that plagues some keepers of nano-tanks is the fact that many people familiar with planted tanks think of Otos as having no bioload. While it’s small enough to be negligible in a tank 10 gallons or larger, it’s not true in a tank as small as 5-gallons.
Otos have a bad reputation for dying quickly. That’s due to two main factors.
The first is that Otos require extremely clean water. Like all suckerfish, they’re native to fast running streams where the water stays in a constant, cleanly state. They will tolerate a wide variety of conditions but large changes can quickly kill them.
The second is a bit more serious: Otos eat a diet consisting of biofilm that grows on underwater plants. This isn’t present in most new tanks, so it’s only safe to add your Otos to an established tank.
The best way to create an environment for them to thrive is to set up the tank for a few months with only invertebrates. Wait until the tank is a completely settled, live environment before adding them. Some Otos will eat algae pellets as well but it’s not a guarantee. There are a few other ways to create biofilm quickly but they’re not suited to anyone who isn’t an advanced aquarist.
Still, if you’re willing to put in the work they’re great accompaniments to planted tanks. And they often surprise people with their lively personalities.
A Couple Options for Brackish Tanks
You’ll be relatively limited if you’re looking to host a brackish tank in this size. Still, there are a couple of suitable options available as long as you’re willing to be careful.
1. Bumblebee Gobies
Bumblebee Gobies are a lively, tiny fish that have a lot of personality despite their small frame. They’re said to reach up to 1.5 inches in size but most of them will remain at or under the 1-inch mark.
Bumblebee Goby are often sold as freshwater fish. That’s not quite the case, as they require brackish water conditions to truly thrive. More than that, they actually require a good amount of plant life as well which means that few of them live to see the 5-year lifespan they enjoy in the wild.
The key to maintaining a successful nano-tank with Bumblebee Gobies is to create the proper environment. That requires the use of many slow-growing plants like Anubias sp. and Java Fern. Watersprite, Hornwort, and Anacharis can be used as well but these plants often grow much too quickly in a 5-gallon tank and can take over.
The fish themselves are easy to care for, lively, and energetic. They simply require plants, a sandy bottom, and the right diet. Most Bumblebee Gobies will ignore pellets and flakes, and success is sometimes mixed with frozen food. Still, a simple brine shrimp hatchery can be made to provide them with a constant diet.
If you’re willing to put in the work and enjoy a unique challenge, Bumblebee Gobies may be right up your alley!
Mollies are actually brackish fish, despite the fact they’re sold as freshwater tropicals. These livebearing fish vary in size from 2-3 inches, making them suitable for a smaller tank as long as only two or three of them are kept.
Avoid the larger subspecies. The Sailfin Molly, in particular, is often found at 3.5” or more when properly taken care of. They’ll be much too large for a 5-gallon tank in short order.
They’re lively and the most intelligent of the various common livebearers available these days.
Mollies prefer a lot of hiding places as well. While only 2-3 of them can be kept in a 5-gallon tank many people have found the addition of a fiddler crab is possible in a nano-tank. They’ll find it virtually impossible to harm the Molly although they will need a space to come above the water. Avoid red-clawed crabs as they can do serious damage to the fish.
Mollies aren’t a challenging fish to keep and they have great personalities. For many, they’re just a way to brighten up a brackish garden. If you’re planning on a larger brackish tank later they’re a great accompaniment to the normal brackish fish that dominate these biome tanks.
Still, in a smaller brackish tank, they can accompany invertebrates like shrimp without too many issues. Give them a shot!
Choose With Care!
A 5-gallon aquarium isn’t too limited when it comes to fish, but the skill required for many can be discouraging. If you’re insistent on starting a nano-aquarium the above fish are all great options but there are certainly others out there. The important thing is to make sure you have a game plan before the fish ever hit the water. So, which of the best fish for 5-gallon aquariums tickles your fancy?