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”.

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. You don’t have to worry, this is a beautiful and simple setup that will amaze you every time it is displayed. 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. 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. You can keep your tank clean by choosing slow-growing plants and animals that aren’t likely to breed quickly. This tank is attractive to everyone because it doesn’t have a lot of different species, but instead looks like a carefully crafted piece of art. The simplicity of its beauty will get people thinking, “Why don’t I do a tank like this?”

Neon Tetras stand out against a wall full of aquatic plants because they have bright blue and red stripes.

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. The male will claim his own territory by providing a pleco cave. To get them ready to spawn, feed the female and male plenty of nutritious foods like Repashy gel food and frozen bloodworms. Once the male has lured the female into his cave to lay eggs, he will continue to fan them 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.

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. 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. Driftwood is a great place to put anubias or Java ferns. The wood also introduces biofilm and mull (or organic matter) that the babies can eat. 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 brighter and can “dance” when they are around females. So make sure you have both genders in your aquarium.

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 – 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. 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. Next, give them powdered foods such Hikari First Bite, Repashy gel foods (in its raw powder form), or 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. You can also add snails, cherry shrimp, and amano shrimp to help clean up any food particles on 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.

If you notice your filter-feeding shrimp eating off the ground, it’s likely that they aren’t getting enough food. So increase their daily portions.

5. The Unheated Aquatic 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. Some cool-temperature invertebrates that would work as tank mates include amano shrimp, Malaysian trumpet snails, nerite snails, and Japanese trapdoor snails. Keep your snails well-nourished with calcium-based foods and enough minerals in their water. 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.