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. These are five of the best setup ideas that we love to share with you.

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

If you are not an expert aquascaper, or a creative artist, it might be difficult to create an exquisite design for your aquarium. This first setup is simple, but it’s a stunning show-stopper every time you look at 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. To maximize impact, drop in 12-20 neon Tetras. 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.) Because it’s not cluttered with different species, this tank looks more like a well-crafted piece 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. To get them ready to spawn, feed the female and male plenty of nutritious foods like Repashy gel food and frozen bloodworms. 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 also keep the parents in a larger aquarium. Once the eggs hatch, transfer the whole pleco cave with the babies into your 20-gallon tank.

When the fry can swim freely, feed them plenty of Repashy gel foods, flake foods and canned green beans. You will need to change the water frequently if you want the fish to stay 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.

To breed, you must have at least one male AND one female. Female bristlenose plecos are more rounded than males.

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). Males are more colorful and will dance in the presence of females. Get both sexes to your aquarium to witness 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. They will happily lay eggs every day if you add lots of floating plants, moses, and other dense leaves. However, you won’t likely see any fry unless the eggs are removed. 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 wood or bamboo shrimp (Atyopsis molucensis), and the vampire shrimp (Atya Gabonensis), have large, feathery hands that are designed to catch and eat small particles in the water. Due to the way they eat, you shouldn’t put up a hang-on-back (HOB), or canister filter that removes every speck 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. You should notice food particles in the aquarium’s water when you add the powder.

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. 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. To create a rainbow of colors, get 12-15 of them.

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. You should ensure that your snails get adequate minerals and are given calcium-based food. 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 have a high energy, beautiful design, and are affordable.