While the mantra for experienced aquarists has long been «bigger tanks are better,» what’s an aquarist to do when they don’t have the space or budget for a large aquarium? If he is looking for an option that has the footprint of a fish tank, but is not as cruel and cramped, then he should consider starting a small nano fish tank.
INTRODUCTION TO NANO TANKS
Freshwater minnows have long been popular choices for community aquariums, but recently the nano tank trend has created new interest in these naturally tiny microfish. Maintaining a nano tank is easier than ever, and I’ll walk you through how to set one up and list the best fish for small tanks.
WHAT ARE NANO TANKS?
One thing that can be confusing is that there is no strict or agreed-upon definition of what makes an aquarium a nano tank. Some people use «nano» to refer to any small aquarium, while others use it specifically for small planted tanks designed as miniature ecosystems.
I’ve noticed that Europeans typically consider any tank under 100 gallons to be a nano tank, while in the US it’s a more commonly used term for tanks under 30 gallons. Therefore, the size of a nano tank can vary considerably around the world and the term can have different meanings depending on where you live.
I’ll stick with the more modern usage, so when I say «nano tank» I mean a 5 to 30 gallon planted aquarium. But building a nano tank involves more than just choosing the capacity of your aquarium. The nano tanks are designed around plants and decoration, with some fish chosen for their color and movement.
NANO TANK BASICS: FISH KEPT IN SMALL AQUARIUMS
It used to be difficult to keep really small planted tanks unless you changed the water several times a week. Even a few fish could overwhelm the system and cause toxic ammonia spikes. Advances in filtration and lighting technology have made maintenance easier, and these small habitats have grown in popularity as a result.
Nano Tank Nitrogen Cycle
The quality of your tank water depends in part on the colonies of good aquarium bacteria that establish themselves in your substrate (and also in the 3-stage filter). Bacteria are an essential part of the nitrogen cycle that converts toxic ammonia from fish waste into nitrates that plants can use as food.
Maintaining water quality in a nano setup can be more difficult than in a larger aquarium because toxins often build up faster than bacteria can break them down. When a small tank crashes from an ammonia overload, it usually happens very quickly and can start losing plants and fish within a few hours.
As with larger tanks, this cycle can take up to three months to establish in a nano tank. To avoid problems with ammonia spikes, I recommend giving your plants a few months to establish before you start putting fish in the tank, and adding them gradually so you don’t lose your balance.
Choosing a Filtration System
Aquarium filters are a must for nano tanks as they remove excess ammonia and keep the water clear and clean. Aquatic plants are more demanding on water quality than most fish species! Using a high quality filtration system such as in-house, submersible, or HOB will protect against sudden changes in water quality.
plants and decoration
Nano tanks are usually designed to mimic a natural habitat like the bottom of a river or lake and are a great place to start if you have an interest in aquascaping. The focus of the tank is on live plants and decorations like rocks, sticks, logs, and other natural materials that create the atmosphere you are looking for.
Nano tanks don’t even have to house fish, although a few fish are usually added to complete the look and give the tank some color. It’s not uncommon for these tanks to have just a lone betta fish or a few algae-eating shrimp or snails!
Illumination systems
After choosing your filtration system, the most important decision you will make when designing a nano tank is choosing a light fixture. Modern aquarium LEDs are an excellent choice for lighting nano tanks because their compact size won’t overpower the tank, but will still provide the light spectrums plants need to thrive.
You may not need a light for your tank, but using one will give you more freedom in choosing your vegetation. You won’t be limited to easy, low-light plants when you have a quality light fixture, and your plants will be better able to use the extra nutrients provided by decomposing fish waste!
temperature and heating
Depending on the temperature range of your home and the type of aquatic animals you would like to keep, you may not need an aquarium heater in your nano tank. Some cold water nano fish do well in room temperature water. But many fish become stressed when their temperature changes by more than a few degrees in a few hours.
I still recommend using a heater in nano tanks that house fish to prevent these sudden changes that can cause stress and illness. Most micro fish prefer warmer water, so you’ll have a lot more options to choose from if you use a heater to maintain a stable temperature.
aquarium substrate
Your aquarium substrate does more than make your tank look good; The substrate supports good bacteria that break down ammonia and provides nutrients and minerals for lush plant growth. Choosing the right substrate to support your plants and fish is key to having a thriving nano tank!
Gravel
Gravel substrates for planted tanks can be fine or coarse and come in a variety of natural shades and colors, from black to earth tones. Avoid using brightly colored neon substrates and choose a type that suits the natural look of your tank. I highly recommend using gravel which improves plant growth!
Your fish may be less fussy about their substrate depending on where they spend their time in your tank. Top -dwelling freshwater fish rarely stay in the bottom parts of your tank, but bottom-dwelling species like catfish may prefer fine gravel or sand to a coarser, more rocky that can damage their delicate chins.
Sand
While sand looks fantastic and fits the natural theme, I don’t consider it an ideal primary substrate for planted tanks as a rule, although many fish prefer the smooth texture. Sand lacks nutrients and minerals and often develops dead zones that can harm bacteria, plants, and aquatic fish.
Using sand on the top layer or for special effects is fine, but I’d stick with a better plant support medium for the bottom layers. Or hide pockets of aquatic soil or gravel in parts of your tank and use sand to create a river effect between them.
water floor
Aquarium floors are an ideal choice for nano tanks. These extremely fine natural or artificial substrates are often packed together with water containing good aquarium bacteria to jump-start the nitrogen cycle. There is no need to rinse or prepare these soils before adding them to your tank and your plants will likely thrive in them!
TIPS FOR CHOOSING FISH FOR SMALL TANKS
Now that you know how to set up a nano tank and enhance your plant growth with the right substrate, lights, and filtration, let’s talk about how to select fish for your new aquarium. What qualities should you look for when storing your tank?
In general, the best choices for nano tanks are fish that:
- They are small in size and do not produce much biological waste (approximately 1 to 3 inches and no more than 5 inches long at maturity)
- Prefers planted or densely planted tanks with lots of hiding places
- They have a peaceful temperament or, if they are aggressive, they can stay happy as a solitary fish
- It won’t gobble up or uproot your plants for fun
- Don’t mind being kept alone or in small groups
I have seen many sites promoting nano shoals for micro tanks. A large school of tetras or corydoras swimming together can have a dramatic impact! But most schooling and shoaling fish only exhibit the behavior in large groups. Nano tanks rarely have room to support the numbers necessary for them to exhibit this behavior.
THE BEST FISH FOR SMALL TANKS: 21 MICRO FRESHWATER FISHES THAT STAY SMALL
What types of small freshwater fish should you consider for your nano tank? You have many options, but these species are especially well suited to small planted tanks and many do well without additional heat in their habitats. From the common to the exotic, here are the best minnows for nano tanks!
betta
The beautiful betta fish is a great choice for nano tanks, and these are some of the easiest fish to care for and an ideal choice for beginners. While male bettas are known for being aggressive and fighting with each other, they do well as a solitary fish or when kept with some similarly sized small finned fish.
Female Bettas can share a tank together in a sorority, although you should try to keep at least 3 to avoid direct competition. May also have a female as a solitary fish or with some peaceful community fish. Both sexes look fantastic in a planted tank and enjoy eating leaves and algae.
| Common name (species) | Betta, Siamese fighting fish (Betta splendens) |
| level of care | Easy |
| Temper | Varies by gender; ideal as a solitary fish |
| Diet | Omnivore |
| average adult size | Females 3.5 inches long Males 5 to 5.5 inches long, depending on variety |
| Minimum tank size | 5 to 10 gallons |
| Temperature | 75 to 86°F |
| pH | 6.0 to 8.0 |
| Schooling species / schools? | Nope |
GUPPY
If you want a group of active micro fish with a wide variety of colors and patterns, consider buying some guppies for your nano tank. These calm fish are sexually dimorphic like the betta but completely non-aggressive. Male fish are smaller than simple females and flash their bright colors as they glide around.
fantasy guppies
It probably comes as no surprise that the Fancy Guppy has long been one of the most popular choices for small aquariums. They are one of the largest guppies and the male fish have elongated fan-shaped tails covered with splashes of bright colors and interesting patterns. Females may also display splashes of color or pattern.
| Common name (species) | Fancy Guppy (Poecilia reticulata) |
| level of care | Easy |
| Temper | peaceful and active |
| Diet | Omnivore |
| average adult size | 1 to 2.5 inches long (females are larger) |
| Minimum tank size | 10 gallons |
| Temperature | 75 to 82°F |
| pH | 5.5 to 8.5 |
| Schooling species / schools? | Yes, but only in larger groups (5 to 10) |
Endler’s Guppies
>Endler ‘s guppies are closely related to the Fancy Guppy, but resemble their wild ancestors in Trinidad. While some sites still list them as a separate species (Poecilia wingei), they are scientifically considered the same as fangs and will freely interbreed with them.
Endlers are smaller and more agile than fancy guppies, and are quite active in a nano tank. Males have short, slightly pointed tails and dots of bright red, blue, orange, and black markings, while females are a fairly flat gray to brown color.
| Common name (species) | Endler’s Guppy, Endler’s Life Bringer (Poecilia reticulata) |
| level of care | Easy |
| Temper | peaceful and active |
| Diet | Omnivore |
| average adult size | 1 to 1.5 inches (females are larger) |
| Minimum tank size | 5 gallons |
| Temperature | 64 to 82°F |
| pH | 5.5 to 8 |
| Schooling species / schools? | Yes, but only in larger groups (5 to 10) |
WHITE CLOUD MINNOW
A nice choice for the center of your tank, the streamlined White Cloud Minnow adds a nice pop of color with its iridescent pink and green scales. These little fish are great for nano tanks, but are often a bit shy when kept in groups of less than 5. The more minnows you have, the more active and outgoing your group will be!
| Common name (species) | White Cloud Minnow, Cardinal fish (Tanichthys albonubes) |
| level of care | Easy |
| Temper | Calm; Usually shy in small groups |
| Diet | Omnivore |
| average adult size | 1 to 1.5 inches long |
| Minimum tank size | 5 gallons |
| Temperature | 64 to 72°F (tolerates up to 78°) |
| pH | 6.0 to 8.0 |
| Schooling species / schools? | Yes, but only in large groups (10+) |
CELESTIAL PEARL danio
>The Celestial Pearl danio adds an impressive amount of color and movement to small planted tanks, and their white-spotted bodies with red or orange fins pop against the vegetation! Male fish are brighter in color and may compete with their mates, so limit their numbers to keep your tank peaceful and provide plenty of hiding places.
| Common name (species) | Celestial Pearl Danio, Galaxy rasbora (Danio margaritatus) |
| level of care | Moderate |
| Temper | Peaceful, active and shy; Male fish can compete for mates, so it’s best to limit their numbers and have 3-5 females per male. |
| Diet | Omnivore |
| average adult size | Up to 1 inch long |
| Minimum tank sizes | 10 gallons |
| Temperature | 73 to 79°F |
| pH | 6.5 to 7.5 |
| Schooling species / schools? | Yes, in groups of 5 or more |
DANISH ZEBRA
The Zebra danio is one of the most researched species in the world and is an ideal choice for community aquariums. These fish are usually silver in color with black stripes, but albino and other color variants are readily available. They do not enjoy being solitary and are happiest in groups of 15+ in larger, heavily planted nano tanks.
| Common name (species) | Zebra Denmark, Zebrafish (Denmark rerio) |
| level of care | Easy |
| Temper | peaceful and active |
| Diet | Omnivore |
| average adult size | 2 inches long |
| Minimum tank sizes | 10 gallons |
| Temperature | 64 to 77°F |
| pH | 6.0 to 8.0 |
| Schooling species / schools? | Yes, but requires a large number (15+) |
RASBORA CHILI
An ideal micro fish for nano tanks is the bright red Chili Rasbora. These fish have distinctive black markings on their body and fins and prefer heavily planted tanks with an acidic pH. They do well in small groups and you can easily fit a school of 6 into a 5 gallon tank! You can also mix them with a community of tetras or minnows.
| Common name (species) | Chili Rasbora, Mosquito Rasbora (Boraras brigittae) |
| level of care | Easy |
| Temper | Calm |
| Diet | Omnivore |
| average adult size | half an inch long |
| Minimum tank sizes | 5 gallons |
| Temperature | 68 to 83°F |
| pH | 4.0 to 7.0 |
| Schooling species / schools? | Yes |
HARLEQUIN RASBORA
>A slightly more complicated option, the Harlequin Rasbora is a tall reddish fish with a black triangle marking on the sides of its body. These fish do not grow very large, but they do need an open space in the center of the tank to swim. They’re a good option for larger nano tanks, but wouldn’t work as well in smaller builds.
| Common name (species) | Harlequin Rasbora (Trigonostigma heteromorpha) |
| level of care | Easy |
| Temper | Calm; shy as a solitary fish or in small groups |
| Diet | Omnivore |
| average adult size | Up to 2 inches long |
| Minimum tank sizes | 10 gallons |
| Temperature | 72 to 81°F |
| pH | 6.0 to 7.8 |
| Schooling species / schools? | Yes, but you need at least 6 in a group |
NEON TETRA
>The ever popular and inexpensive Neon Tetra is a great choice for community and nano tanks. These silver, blue, and red fish are sensitive to changes in water quality and are best added a few months after your tank is cycled. This is a popular option if you want them to go to school, but you’ll need at least 15 neons in a 20-gallon setup to see behavior.
| Common name (species) | Neon Tetra (Paracheirodon innesi) |
| level of care | Easy |
| Temper | Peaceful and active; can be shy in small amounts |
| Diet | Omnivore |
| average adult size | 1 to 1.5 inches long |
| Minimum tank size | 10 gallons, but 20 gallons is ideal for a group of 15 |
| Temperature | 70 to 81°F |
| pH | 6.0 to 7.0 |
| Schooling species / schools? | Yes, but only when kept in larger groups of 15 or more |
CARDINAL TETRA
>If a fish looks like a neon but has a red stripe running the length of its body, then it must be the nearly identical and closely related Cardinal Tetra. Cardinals tend to grow slightly larger than neons, but their care and requirements are the same. You can keep a few, but their behavior is more interesting in larger groups.
| Common name (species) | Cardinal Tetra (Paracheirodon axelrodi) |
| level of care | Easy |
| Temper | Peaceful and active; can be shy in small amounts |
| Diet | Omnivore |
| average adult size | 1.5 to 2 inches long |
| Minimum tank size | 10 gallons, but 20 gallons is ideal for a group of 15 |
| Temperature | 73 to 81°F |
| pH | 6.0 to 7.0 |
| Schooling species / schools? | Yes, but only when kept in larger groups of 15 or more |
TETRA MAN
If you want to add pops of color to your nano tank, the diminutive Ember or Fire Tetra might be just the thing for you! These bright red fish thrive in densely planted environments and do well in small groups of 6 to 8. You’ll see them swimming and foraging, and they usually stick to the center of your tank and avoid the bottom and top areas.
| Common name (species) | Ember tetra, fire tetra (Hyphessobrycon amandae) |
| level of care | Easy |
| Temper | Peaceful, active and playful |
| Diet | Omnivore |
| average adult size | 0.5 to 0.8 inches long |
| Minimum tank size | 10 gallons |
| Temperature | 68 to 82°F |
| pH | 5.5 to 7 |
| Schooling species / schools? | Yes, when kept in groups of 6 to 8 |
BLUE-FINNED NOTHO
>If you want something out of the ordinary, then the colorful Bluefin Notho could be a unique choice for your larger nano tank. Their red bodies are dotted with blue highlights and they look amazing against your greenery. They are a bit more difficult to keep due to their limited temperature range, but are generally an excellent choice for planted aquariums.
| Common name (species) | Bluefin Notho, Rachovi’s Killifish (Nothobranchius rachovii) |
| level of care | Easy to Moderate |
| Temper | Calm |
| Diet | Carnivore prefers live food |
| average adult size | Up to 2.25 inches long |
| Minimum tank size | 20 gallons |
| Temperature | 72 to 75°F |
| pH | 6.0 to 7.5 |
| Schooling species / schools? | Nope |
pygmy corydoras
An interesting option for a dwelling at the bottom of the mid-level fish is the Cory pygmy cat. These black-marked silverfish are one of the few catfish that pack a punch when kept in groups of 4 to 8. They are easy to care for and thrive in planted tanks. They do well as solitary fish and in mixed communities as they get along well with other species.
| Common name (species) | Pygmy corydoras, pygmy catfish (Corydoras pygmaeus) |
| level of care | Easy |
| Temper | peaceful and active |
| Diet | Omnivore |
| average adult size | Up to 1 inch long |
| Minimum tank size | 10 gallons |
| Temperature | 72 to 79°F |
| pH | 6.0 to 8.0 |
| Schooling species / schools? | Yes, when kept in groups of 4 to 8 |
MAGICAL CORYDORAS
>The Spotted Sixray Cory cat is a bit difficult to handle because the rays on its dorsal fin are very sharp and can pierce the skin. You should only handle this fish with a plastic container for your own safety, because their bones get caught in the nets. These small bottom feeders need a soft substrate and prefer to be kept in groups of at least 5.
| Common name (species) | Sixray Corydoras, False Cory Cat (Aspidoras pauciradiatus) |
| level of care | moderate to difficult |
| Temper | Peaceful but sharp rays can accidentally pierce other fish, so they are best kept as the only bottom feeder in a tank |
| Diet | Omnivore |
| average adult size | 0.8 to 1.2 inches long |
| Minimum tank size | 10 gallons |
| Temperature | 72 to 77°F |
| pH | 6.0 to 7.2 |
| Schooling species / schools? | Shallows and prefer to live in groups of 5 or more |
catfish otocinclus
>Whether or not you have an algae problem, adding Catfish otocinclus to a nano tank makes a lot of sense. These tiny algae-eating machines are easy to care for and they also chew up decaying vegetation, making them an ideal companion for cleaning out a planted tank! If you keep some Ottos together, they will often hang out and even go to school.
| Common name (species) | Otocinclus catfish, Ottos, dwarf sucking catfish (several species, including otocinclus vestitus) |
| level of care | Easy |
| Temper | peaceful and active |
| Diet | Herbivorous; eats mainly algae and decaying leaves |
| average adult size | 1 to 2 inches long |
| Minimum tank size | 10 gallons |
| Temperature | 72 to 82°F |
| pH | 6 to 7.5 |
| Schooling species / schools? | Yes, when kept in groups of 4 to 6 |
SALT AND PEPPER CATFISH
If you want some small fish with outgoing personalities, consider a group of Salt and Pepper Cory Cats for your larger nano tank! These silver and black bottom dwellers are one of the smallest and most social catfish, and love to explore your plants and décor. They are easy to care for in groups of 6 to 8 and are an ideal choice for community tanks 15 gallons or larger!
| Common name (species) | Salt and Pepper Catfish, Salt and Pepper Cory Cat (Corydoras habrosus) |
| level of care | Moderate |
| Temper | Peaceful, active and social; best kept in groups of 6 or more |
| Diet | Omnivore |
| average adult size | 1 to 1.5 inches |
| Minimum tank size | 15 gallons |
| Temperature | 71 to 84°F |
| pH | 6.0 to 7.7 |
| Schooling species / schools? | Nope |
ASIAN STONE CATFISH
Another unique bottom feeder is the Asian spiny catfish. These interesting brown, tan, and black fish are covered in long pectoral spines and blend in with their tank surroundings. They do a great job of cleaning up food debris from the substrate and prefer to live in small groups of three or more. However, it is best to keep them as the only bottom dwellers, as larger fish may eat all of your food.
| Common name (species) | Asian stone catfish, dwarf moth catfish (Hara jerdoni) |
| level of care | Easy |
| Temper | peaceful scavenger |
| Diet | Omnivore |
| average adult size | Up to 1.5 inches long |
| Minimum tank size | 5 gallons |
| Temperature | 64 to 75°F |
| pH | 5.6 to 7.6 |
| Schooling species / schools? | Nope |
PEA BLOBE FISH
I have always been fascinated by puffer fish, and the little Pea or Dwarf Puf
