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5 Best Fish Tank Ideas for a 20-Gallon Aquarium

Getting a new 20-gallon aquarium is like starting with a fresh, blank canvas. There are so many possibilities when it comes to choosing the decorations, live plants, and of course aquarium fish. If you’re stuck in analysis paralysis from all the choices, here are five of our favorite setup ideas to help inspire you.

1. The “I Just Want It to Look Good” Aquarium

Unless you’re an expert aquascaper or creative artist type, it may be difficult for you to come up with an intricately beautiful design for your aquarium. Not to worry – this first setup is a simple but stunning showstopper every time you see it. The goal is to fill the back half of the aquarium with plants of all different textures and colors, such as java fern, stem plants, vallisneria, or a dwarf aquarium lily. Then drop in a school of 12 to 20 neon tetras for maximum impact. There’s something instantly mesmerizing about seeing a large group of identical fish swimming in an underwater forest of plants.

Neon tetras tend to swim in the middle of the aquarium, so you can add a few bottom dwellers to round out the community, such as a red cherry shrimp colony that pops against the greenery, three to four kuhli loaches to clean up the tank at night, or a few nerite snails for algae control. (For minimal tank maintenance, choose slow-growing plants and animals that won’t breed too quickly.) Everyone is drawn to this setup because it isn’t jumbled with a dozen different species but rather looks like an carefully crafted work of art. The simplicity of its beauty will get people thinking, “Why don’t I do a tank like this?”

neon tetra planted tank

Neon tetras have bright blue and red stripes that really stand out against a wall of aquatic plants.

2. The “Fish Breeding” Aquarium

Setting up a dedicated tank for breeding fish is enjoyment for the whole family. You can teach kids about nature, get your partner more interested in aquariums, and even sell the offspring to your local fish store or other hobbyists for profit. Most people start with livebearers (or fish who bear live young) like guppies or platies, but have you ever considered breeding bristlenose (or bushynose) plecos before? Many varieties – such as wild-type brown, albino, super red, calico, and long fin bristlenose plecos – have been developed because they are so easy to breed. Just provide a pleco cave for the male to claim as his own territory. Feed the male and female lots of nutritious foods, like frozen bloodworms and Repashy gel foods, to get them ready for spawning. Then the male will entice the female to his cave, trap her inside to lay eggs, and faithfully fan the eggs (to increase water flow) until they hatch. If you wish, you can keep the parents in a larger community aquarium, and within two days of hatching, move the entire pleco cave (with the babies) into your 20-gallon tank as a safe haven to raise them.

Once the fry are freely swimming, provide plenty of food in the form of Repashy gel food, flake foods, canned green beans, frozen baby brine shrimp, and even algae in your tank. Of course, lots of food means you must do lots of water changes to keep the water clean and the fry healthy. To decrease the buildup of nitrogen waste (and make the aquarium look better), consider adding live plants to the aquarium. Java fern and anubias attached to driftwood provide cover for the babies, and the wood introduces biofilm and mulm (or organic debris) for them to snack on. Once they are about 2 inches (5 cm) long, you can move a few of your favorites to other aquariums to help with algae control and sell the rest to your local fish store. Now your 20-gallon aquarium is ready for the next breeding project. 

bristlenose pleco

In order for breeding to occur, you need at least one male and one female. Male bristlenose plecos tend to have a very bushy snout, whereas females have a smoother face.

3. The Rainbowfish Aquarium

Most rainbowfish are too big to fit comfortably in a 20-gallon fish tank, but it’s the perfect size for rainbowfish in the Pseudomugil genus and other dwarf rainbowfish that remain under 2-2.5 inches (5-6.3 cm) long. Some of the most popular species include the neon red (P. luminatus), forktail blue-eye or furcata (P. furcatus), spotted blue-eye (P. gertrudae), Celebes (Marosatherina ladigesi), and threadfin rainbowfish (Iriatherina werneri). The males are more colorful and will “dance” in the presence of females, so get both sexes for your aquarium to see this unique behavior.

As surface-dwelling fish, rainbowfish inhabit the top one-third of aquariums, so make sure to have a tight-fitting tank lid that prevents them from jumping out. Add lots of floating plants, mosses, and other dense foliage because they’ll happily lay eggs every day (although you probably won’t see any fry unless you remove the eggs). Because of their small mouths, feed them tiny floating or slowly sinking foods, such as baby brine shrimp, daphnia, cyclops, crushed flakes, micro pellets, and Easy Fry and Small Fish Food.

Dwarf rainbowfish can be a tad more expensive at $10 to $15 each, and ideally you want a school of six or more. To fill out the rest of the tank, you can get other community fish like small tetras and rasboras that swim in the middle and corydoras and snails that scavenge at the bottom. (Cherry shrimp may get picked on since rainbowfish are active creatures that love to eat.)

neon red rainbowfish

While dwarf rainbowfish can be a little harder to source, keep searching because their gorgeous colors and lively behavior are worth the hunt.

4. The Oddball Aquarium

Most people think of oddballs as rare or interesting fish, but what about keeping an oddball invertebrate? Filter-feeding shrimp – like the bamboo or wood shrimp (Atyopsis moluccensis) and vampire shrimp (Atya gabonensis) – have large, feathery mitts on their hands that are made for catching and eating small particles floating in the water. Because of the way they feed, don't set up a powerful hang-on-back (HOB) or canister filter that polishes all the little crumbs from the water. Instead, go with a gentle sponge filter or maybe just an air stone with lots of sturdy plants for them to climb on. Then give them powdered foods like Hikari First Bites, Repashy gel food (in its raw powder form), and specialty foods for filter-feeding shrimp. When you feed the powder, the aquarium should get slightly cloudy with food particles visibly swirling in the water.

For a 20-gallon fish tank, you can get one to two bamboo shrimp and one vampire shrimp. The shrimp grow rather large, ranging from 3-6 inches (8-15 cm) each, so you want them to stand out as the centerpieces of the aquarium by pairing them with nano fish like celestial pearl danios, Norman’s lampeye killifish, and chili rasboras. Also, consider adding some snails, amano shrimp, or cherry shrimp to clean up the food particles that fall to the substrate. If you’re searching for a different kind of community tank that will make people look twice, this weird, invertebrate-centric tank may be right for you.

bamboo shrimp

If you see your filter-feeding shrimp scavenging on the ground, they’re likely not getting enough food, so increase their daily portion size.

5. The Unheated Aquarium

Looking for fish that can live in a 20-gallon tank with no heater? If your room temperature is 62°F (17°C) and above, then this danio aquarium may be the perfect choice. Danios are a highly active, torpedo-shaped fish that come in many varieties and colors, such as zebra, leopard, long fin, and even Glofish. Get 12 to 15 of them to create a kaleidoscope of colors zooming around the tank and going crazy during feeding times.

Danios swim at all layers of the aquarium, but you can add some other species that like cooler waters, such as five or six salt and pepper corydoras to pick up any food that gets past the danios. Some cool-temperature invertebrates that would work as tank mates include amano shrimp, Malaysian trumpet snails, nerite snails, and Japanese trapdoor snails. (When keeping snails, make sure they get enough minerals in the water and are fed some calcium-based foods.) If you want an action-packed, beginner-friendly tank full of hardy fish, you can’t go wrong with an aquarium of danios.

longfin zebra danio

Long fin zebra danios are very popular because of their high energy, beautiful pattern, and low cost.

For more fish stocking ideas and inspiration, check out our article on 7 Popular Fish You Should Try in a 20-Gallon Aquarium.


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