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 at “I Just Want It to See 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. This first setup is simple, but it’s a stunning show-stopper every time you look at it. The aim is to fill the back of the aquarium with plants in a variety of textures and colors. 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 nerite snails to control algae. (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. People will be inspired by its simplicity and beauty to create their own tank.

Neon tetras feature bright blue and contrasting red stripes, making them stand out in a sea 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, super-red, albino, calico and long-fin bristlenose plecos, have been developed. The male will claim his own territory by providing a pleco cave. Give the male and female Repashy gel foods and frozen Bloodworms to help them prepare for spawning. 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.

Provide plenty of food for the fry, including Repashy, flake and frozen baby brine shrimps, canned green beans, canned green beans, and algae. You will need to change the water frequently if you want the fish to stay healthy. Live plants can be added to aquariums to reduce the amount of nitrogen waste and improve the aquarium’s appearance. 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. Your 20-gallon aquarium can now be used for breeding.

In order to breed, at least one male must be present and one female must also be present. Bristlenose pleco males have a bushy snout while females have a smoother, more round 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). Males are more colorful than females and will “dance” when they’re around them. 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. If you don’t remove the eggs, they will lay eggs every single day. 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 (Atyopsismoluccensis), and vampire shrimps, have large, feathery fingers that are used to catch and consume small particles in water. You shouldn’t use a canister or hang-on back filter to remove all the crumbs. 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. This weird, invertebrate-centric community tank might be the right choice for you if you are looking for something different.

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 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. Get 12 to 15 of them to create a kaleidoscope of colors zooming around the tank and going crazy 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. Some cool-temperature invertebrates that would work as tank mates include amano shrimp, Malaysian trumpet snails, nerite snails, and Japanese trapdoor snails. Make sure snails are getting enough minerals from the water, and that they are being fed 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 have a high energy, beautiful design, and are affordable.