Nano aquariums are beautiful, but choosing the right fish for them can be tricky. Since tanks under 20 gallons don’t offer much space, you’ll want to select species that stay small, remain peaceful, and thrive in compact environments. Making careful choices ensures a vibrant, balanced ecosystem without overcrowding.
Here are ten of the best fish for a nano reef aquarium — each offering its own unique personality, beauty, or benefits.
1. Shrimp Goby & Pistol Shrimp Pair
Few relationships in the aquarium world are as fascinating as the partnership between a shrimp goby and a pistol shrimp. These two form a symbiotic bond: the nearly blind shrimp digs and maintains a shared burrow, while the goby provides food and protection. You’ll often see the goby stationed at the entrance as the shrimp works, using its antenna to stay connected. Watching this duo interact is like having a little nature documentary unfold in your tank.
2. Barnacle Blenny
Barnacle blennies are tiny but endlessly entertaining. They wedge themselves into small crevices in the rockwork, poking their heads out as if standing guard. While they tend to stay hidden most of the time, feeding brings them to life — they’ll dart out at lightning speed to grab food before zipping back to their hole. Their quirky behavior makes them a fun addition, even if they’re not always swimming in open view.
3. Possum Wrasse
Most wrasses grow too large or act too aggressively for a nano system, but the possum wrasse is an exception. Peaceful and small, it makes a great candidate for compact setups. They may be shy when first introduced, but over time, they’ll become more active and comfortable. For best results, keep them with other peaceful tankmates in a well-established aquarium.
4. Tailspot Blenny
The tailspot blenny combines charm with utility. Known for their curious personality, they spend much of their day grazing on algae. This natural appetite can help keep nuisance algae under control, making them a helpful part of your cleanup crew. If your tank lacks algae, supplement their diet with algae-based foods to keep them healthy.
5. Clown Goby
Reaching only about 1.5 inches, clown gobies pack a lot of character into a tiny package. Their big heads and bright color variations make them particularly endearing. While they’re perfect for smaller systems, they have a reputation for nipping at SPS coral polyps, so it’s best to house them with soft corals or LPS corals instead.
6. Geometric Pygmy Hawkfish
Despite its name, this fish actually belongs to the anthias family but behaves much like a hawkfish. It hops around the aquarium with great personality, yet only grows to about 2 inches. Unlike larger hawkfish, it usually poses less risk to shrimp, though it may be aggressive toward very small gobies or blennies. Tankmate selection is key here.
7. Flaming Prawn Goby
One of the most striking nano gobies, the flaming prawn goby dazzles with its beauty. However, they’re notoriously shy, especially at first. With time and patience, they’ll venture out more often. Their small size (1–1.5 inches) and delicate nature mean they should only be kept with the most peaceful companions.
8. Court Jester Goby
If you want a fish that works double duty as both a display and a cleaner, the court jester goby is a great choice. Constantly sifting sand and picking at algae, they’re particularly fond of hair algae. These gobies often rely on natural foods over prepared diets, so placing them in a mature aquarium is best.
9. Orange-Striped Cardinalfish
Known for their calm demeanor, orange-striped cardinals are among the most peaceful fish for a nano reef. Even though they can grow up to 3 inches, their slow swimming and non-aggressive behavior make them perfectly suited for smaller systems. While they can be kept in groups in larger aquariums, stick with one in a nano tank.
10. Pink Firefish
For a burst of color and graceful swimming, the pink firefish is a favorite. They hover elegantly in the water column, often retreating to rockwork when startled. Because they’re prone to jumping if spooked, a secure lid is essential. With proper tankmates and cover, they’ll thrive and add a striking visual element to your reef.
Final Thoughts
Stocking a nano reef takes care and restraint — but with the right choices, you can enjoy an aquarium full of life and personality. Each of these species brings something special, whether it’s utility, color, or sheer entertainment value. By choosing fish that fit your tank’s size and temperament, you’ll create a thriving environment that’s both balanced and beautiful.
