A Big, Small Change: Starting a Freshwater Nano Tank

Author: Mark Denaro 

Nano tanks are all the rage in the aquarium hobby these days, attracting a new audience to this popular pastime. While the size and convenience of these tiny tanks may give the impression of being foolproof, there are several factors to consider before setting one up. These concerns are similar to those when maintaining a larger system but become critical to the survival of a smaller system.

Nano Tank Basics

Many of the nano tanks on the market today are sold as kits that include lighting and filtration. Although this can offer new hobbyists an easy start, it may be problematic for the advanced aquarist looking to join in on the nano trend. In some cases, the lighting will not be sufficient for a planted tank, and plants and nanos seem to go hand in hand, especially when it comes to freshwater setups. However, some of these kits are specifically designed for planted tanks, and these are better choices for experienced hobbyists.

Nano kits intended for marine aquarists may also be an excellent alternative for those seeking a pre-assembled unit for a planted freshwater setup, as they generally include integrated filtration and higher-quality lighting. Logically, if the lighting will maintain corals, it will also maintain plants. There’s a myth out there about actinic lighting and plants, but it’s not true; this type of lighting is actually beneficial to freshwater plants, and scientific evidence demonstrates that they utilize wavelengths in the actinic range.

While kits may be a good place to start, especially for new hobbyists, the rest of us may want to seek out smaller tanks that are sold separately. Some companies offer a variety of sizes, including deep, cube-shaped ones that will work quite well for our freshwater purposes.


Because we’re dealing with small volumes of water, filtration is critically important. Nano tanks can experience rapid shifts in water quality. Changing or cleaning your filter frequently can be a cornerstone to success with a small aquarium. Similarly, placement is another important factor that will have a direct impact on the health of your tank. Ideally, it should be kept where it will not be affected by cold drafts or receive direct sunlight, as this can significantly alter the water temperature. The aquarium must also be level and well supported; a dedicated stand or sturdy piece of furniture works well.

Regular maintenance is one of the most important considerations in the long-term success of a nano aquarium. Water changes should be performed at least weekly and preferably more frequently. Siphon out any detritus from the bottom of the tank. While some people don’t like to disturb the substrate in planted aquaria, I suggest vacuuming the top layer to help eliminate the potential for problems to develop over time due to the buildup of organic waste. Monitor water temperature during changes and adjust the new water to the same temperature as that in the aquarium. Large shifts in water temperature due to the addition of hot or cold water can have detrimental impacts on the well-being of all the inhabitants.

Lighting can make or break any aquarium, but the correct choice is of even greater importance in nano tanks. Avoid any light source that creates a fair amount of heat. The best choice is LED lighting. There is a tremendous range of LED lighting fixtures on the market, and many are customizable for the amount of light and spectral output they produce. The light spectrum and intensity you choose depends on what you plan to keep in the tank.


Now that we’ve sorted out equipment concerns, the real fun can begin. Because freshwater nano tanks are great for creating microhabitats, the next consideration is which plants you should add. Any of the bunch or stem plants can be successfully maintained, but those that grow quickly need to be pruned more frequently. Still, this group offers many choices that provide a variety of shapes and colors. Most of these work best as background or midground plants, and include Mayaca fluviatilisHemianthus micranthemoidesAlternanthera reineckii “Lilacina,” Bacopa monnieriRotala indica, and most of the Ludwigia species.

The genus Cryptocoryne offers myriad choices, and over time many of these will spread to fill in an area with dense growth. I frequently use Cryptocoryne beckettiiC. beckettii var. “petchii,” C. affinisC. pygmaeaC. nevillii, and of course all the various forms of C. wendtii. If you want to create a “lawn” in the foreground, your options include the various chain swords, such as Echinodorus tenellus, as well as dwarf Sagittaria spp. or Glossostigma elatinoides. I also like to use the four-leaf clover, Marsilea crenata, in the foreground. Smaller species of Nymphaea can make very effective focal points or can be allowed to form floating pads. The best choices are Nymphaea rubra and N. micrantha. Smaller Anubias species, such as Anubias barteri var. “nana” or “nana petite,” can also be particularly effective.

Plant fertilizers are important in keeping plants healthy in a freshwater nano tank; I always dose them on a daily basis. The idea is to keep the system nutrient poor, much in the manner that reef hobbyists run their systems. The directions on the bottles of many plant fertilizers recommend adding them weekly, biweekly, or (at most) twice a week. The problem with this approach is that it adds more nutrients than the plants can absorb in a short time, meaning that more is available for any algae present to utilize. Determine the amount of fertilizer that should be added to your tank each week and divide it by seven. This is the amount that should be dosed each day. By dosing in this manner, the plants will outcompete the algae for available nutrients, which will control algae growth. Whether your tank is heavily or lightly planted, adjust the manufacturer’s recommended dosage to suit it.


When it comes to stocking, many species will do well in your little tank. One of the best genera for a freshwater nano is Boraras. All the Boraras species make great choices, but my particular favorite is Boraras brigittae, commonly known as the chili or mosquito rasbora. This fish is a living jewel, with an orange pattern that just seems to glow with an inner radiance when it is well settled into a planted aquarium. Another favorite is the galaxy danio (Danio margaritatus). This colorful, pearl-dotted fish took the hobby by storm a few years ago and remains one of the most beautiful selections available to this day.

The cichlid family is one of the most popular in the hobby, and several of these fish will fare well in small aquariums. This list starts with the genus Apistogramma, as most of its 200-plus members make for suitable choices. In particular, the two most readily available species, Apistogramma agassizii and A. cacatuoides (including all their geographic variants and captive-bred color morphs) make excellent additions to freshwater nanos. For those preferring Old World cichlids, many of the shell dwellers from Lake Tanganyika are a viable alternative.

Livebearer fanciers also have a number of choices for the planted tank . Endler’s livebearers (Poecilia wingei) are another great option for the planted tank. For more advanced hobbyists, Micropoecilia spp. can present a bit of a challenge but do well in a nano setup.

All but the largest species of killifish do well in community or biotope nano tanks with appropriate tankmates, though species with long fins may present too tempting a target for other fish. Use a tight-fitting cover or the killies may not stay in the tank.

While we’re on the subject of jumping fish, I would be remiss in not mentioning bettas. You can add a single specimen of the domesticated Betta splendens in any finnage type and color that floats your boat, but why not try a pair or small group of one of the coccina complex species? Collectively known as dwarf red fighters, these diminutive fish can be maintained in groups and thrive in nano tanks.

Of course, you’ll need some bottom dwellers, and members of the genus Corydoras fit the bill. In particular, the three smallest species, Corydoras pygmaeusC. hastatus, and C. habrosus, are great choices, but don’t forget those that grow just a bit larger, such as C. panda and the rare but super cool C. gracilis.

It seems that every month brings a new shrimp species or color morph into the hobby, and many are suitable for these freshwater setups. However, careful consideration must be made when including shrimp in a freshwater nano tank to ensure they will not be eaten by the fish. Some predation on the juveniles is almost inevitable, but they reproduce quickly enough that any loss should not be significant. In particular, the various color morphs of the cherry shrimp (Neocaridina davidi) are wonderful additions, but your choices are not limited to this species since many others are always appearing in the trade. Second in popularity to the cherry shrimp is the crystal shrimp (Caridina cantonensis) and their various morphs. However, do not mix color morphs of the same species of shrimp, as they will crossbreed and the resulting offspring are usually of poor quality and color.

Additionally, consider the Mexican dwarf crayfish (Cambarellus patzcuarensis). This little invertebrate is plant and fish friendly and only reaches a size of about 2 inches (5 cm). However, some areas have restricted crayfish sales, and C. patzcuarensis is considered an endangered species. If you want to keep snails, your best bet will be members of the genus Neritina, which require brackish water for successful development of their young. A number of species are available, of which my favorite is the zebra nerite snail (Neritina natalensis).

Don’t Overfeed Your Fish

Because we’re dealing with small volumes of water, it is very important not to overfeed the fish and other tank inhabitants. Use only the best-quality foods you can find and provide them sparingly. Despite what the directions on the flake or pellet container may say, feed only the amount of food that can be consumed in 60 seconds. Feed several times a day if you want to, but control the portions to be sure that anything uneaten is not breaking down or rotting in the aquarium and causing problems. If you choose to add some type of algae wafer or gel-based diet that is intended to be consumed over a longer time period, then this rule does not apply.

Research Fish Species Before Buying

There are hundreds of fish, invertebrates, and plants that are suitable for inclusion in freshwater nano systems. It is always a good idea to research species that interest you before purchasing them, but it is an absolute necessity with these tanks. Make sure that the species you select are suitable in terms of both size and temperament to prevent future problems with compatibility or space. Also look for information regarding their preferred water conditions and temperature to be sure that all the inhabitants can happily and comfortably live together.

Remember to keep up with maintenance and spend some time monitoring the system on a daily basis. Apart from being one of the most enjoyable aspects of the hobby, observation will help you to notice problems as they begin to develop rather than after they’ve blossomed into full-scale emergencies. Conditions in nano tanks can change quickly, so careful observation and regular maintenance are the keys to success.