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. Here are five of our favorite setups to inspire you if you find yourself stuck in analysis paralysis due to all the options.

1. The Aquarium with the “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.

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 maintenance, you should choose slow-growing plants or animals that don’t reproduce too fast. 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. People will be inspired by its simplicity and beauty to create their own tank.

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? Because they are easy to breed, many varieties have been created, including wild-type brown, albino and super red plecos. 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. 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. 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. Adding live plants to your aquarium can help reduce nitrogen waste buildup and make it look better. 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. You are now ready to start your next breeding project with your 20-gallon aquarium.

In order for breeding to occur, you need at least one male and one female. The male bristlenose plecos have a bushy nose, while the females have a more smooth 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. 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 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. 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. Next, give them powdered foods such Hikari First Bite, Repashy gel foods (in its raw powder form), or specialty foods for filter feeding shrimp. The aquarium will become cloudy from the food particles being dissolved 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. This weird, invertebrate-centric community tank might be the right choice for you if you are looking for something different.

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 Aquarium

Looking for fish that can live in a 20-gallon tank with no heater? If your room temperature is 62degF (17degC) 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. You can get anywhere from 12 to 15 to make a kaleidoscope, zooming around your tank and getting wild during feeding times.

Danios can swim in all aquarium layers. However, you can add other species that prefer cooler water, such as five to six salt and pepper corydoras, to grab any food that passes the danios. Cool-temperature invertebrates such as amano shrimp, Malaysian whistle snails and nerite snails would be good tank mates. 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.