5 Best Fish Tank Ideas for a 20-Gallon Aquarium

A 20-gallon aquarium can be like a 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 Aquarium “I Just Want It to Look Good”.

It may not be easy to design an aquarium that is beautiful and intricate if you aren’t an aquascaper or an artist. Not to worry – this first setup is a simple but stunning showstopper every time you see it. You want to fill the aquarium’s back with plants of different textures and colors. This could include stem plants, vallisneria or dwarf aquarium lilies. For maximum impact, add a group of 12-20 neon tetras. There’s something instantly mesmerizing about seeing a large group of identical fish swimming in an underwater forest of plants.

You can add some bottom dwellers to the aquarium to make them more interesting. For example, a colony of red cherry shrimp that stands out against the greenery, a few kuhli loaches for night cleaning, and a few nerite shells to control algae. (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 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? They are so easy-to-breed that many varieties, such as the wild-type, albino, super-red, and long-fin bristlenose plecos, have been developed. You should provide a pleco cave that the male can claim as his territory. Feed the male and female lots of nutritious foods, like frozen bloodworms and Repashy gel foods, to get them ready for spawning. The male will then lure the female to his cave and trap her inside. Once she has laid eggs, the male will keep the eggs in the water, increasing the flow of water until they hatch. You can place the parents in an aquarium that is larger than your home. After the babies hatch, move them all into your 20 gallon tank.

After the fry have learned to swim, you can provide them with plenty of food such as Repashy gel food and flake food. You will need to change the water frequently if you want the fish to stay healthy. Adding live plants to your aquarium can help reduce nitrogen waste buildup and make it look better. Anubias and Java fern attached to driftwood provide cover and food for the babies. 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.

In order to breed, at least one male must be present and one female must also be present. 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. You can add lots of floating plants and mosses to encourage them to lay eggs daily, although you may not see any fry until you take out 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.)

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 such as the bamboo or wood shrimps (Atyopsis Moluccensis), and vampire shrimps (Atya gabonensis), are equipped with large, feathery mitts that can catch and eat small particles suspended in the water. You shouldn’t use a canister or hang-on back filter to remove all the crumbs. You can use a sponge filter, or an airstone with plenty of plants to help them climb on. You can then give them powdered foods such as Repashy gel food, Hikari First Bite and other specialty foods that are suitable 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. To clean up food particles from the substrate, you might also consider adding snails, amano shrimp or cherry shrimp. This weird, invertebrate-centric community tank might be the right choice for you if you are looking for something different.

If your filter-feeding shrimp are scavenging on ground, then they probably don’t get enough food. Increase their daily portion.

5. The Unheated Aquarium

Looking for fish that can live in a 20-gallon tank with no heater? This danio aquarium is ideal for those who live in rooms that are at least 62 degrees F (17 degrees C) or higher. Danios are a highly active, torpedo-shaped fish that come in many varieties and colors, such as zebra, leopard, long fin, and even Glofish. You can get anywhere from 12 to 15 to make a kaleidoscope, zooming around your tank and getting wild 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. Amano shrimps, Japanese trapdoor snails, nerite and Malaysian trumpet snails are all cool-temperature invertebrates which would make good tank mates. (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.

Long fin Zebra danios are extremely popular due to their beautiful patterns, high energy and low cost.