Updated: November 3, 2020 - By: - Categories: Starter guide

A twenty-gallon aquarium is a perfect sized tank for those wishing to start keeping tropical fish, it is large enough for a small community (depending on the species you wish to keep) and is also ideal as a quarantine or hospital tank.

Best 20-gallon aquarium review

Let’s take a look at some of the 20-gallon aquariums available to buy, we’ll talk through the features of each one so that you can best decide which one will suit you best.

Marina LED Aquarium Kit 20-gallon

The Marina LED Aquarium Kit is an ideal tank for a beginner interested in keeping fish. It comes with most things you will need for the setup process. They include a rimmed glass tank with LED hood, Marina Slim clip-on filter with cartridges, water conditioner (to treat tap water), tropical flakes, biological supplement (to boost the Nitrogen cycle), fishnet, stick-on thermometer, and care guide.

What I love best in this kit is its filter with quick-change cartridges. The cartridges are floss pads included with activated carbon and ceramic to perform three-stage filtration with mechanical, biological, and chemical. It is very efficient in keeping the water clean, clear, and free of Nitrogenous toxics.

The LED lighting, which is housed within the hood, is energy-efficient so the running cost is reduced; this white LED lighting is also suited for live plants if you wish to keep some within the tank.

It is a complete setup if you wish to house coldwater fish. It doesn’t come with a heater, simply add a 100-watt heater and you can then keep tropical livestock.

Aqueon LED Aquarium Kit 20 Gallon

This 20-gallon tank is ideal for those wishing a full set-up. Within this product, you’ll find most items needed to keep freshwater tropical fish. There are a QuietFlow 10 PRO power filter, 100W heater, fish food, water conditioner, fishnet, and a thermometer.

The main tank is a standard shape and comes with a black lid. The black hood consists of a feeding hatch and LED lighting.

The filter is a hang-on one that is perfectly sized for this tank. It is able to alert you, with a red light, when its cartridge needs to be replaced (one included).

The heater is a preset one and holds a temperature of 78 degrees; so, ensure any livestock kept in this aquarium that requires heat is suited to this exact temperature if you intend on using this heater.

Tetra Aquarium 20 Gallon Fish Tank Kit

This aquarium starter kit is 20-gallons and an ideal set-up for those starting in aquarium keeping.

It is a beautiful tank, classically shaped, and comes with everything needed to get you started. Its edges are well sealed with clear silicone, and the base and top are reinforced with black rims for durability and a longer lifetime.

The kit comes with an LED hood, Tetra Whisper 20 Hang-On-Back filter, preset heater, and some decorations. The LED lighting unit is energy efficient and is designed to mimic natural sunlight.

If purchasing this starter tank, you’ll also gain access to Tetra Care, which provides you with free help and advice in running an aquarium.

Aqueon 20 Gallon Long Aquarium

This 20-gallon tank is suitable for both freshwater and marine setups. It is a long tank that means it provides more contacting space between the surface water and the air, compared to a high/standard form. This makes it better for stocking fish.

This longer sized tank is suitable for species that prefer swimming space on the surface like Zebra Danios, Guppies,… It is also ideal if you plan to keep bottom-dwellers; such as small Corydoras, shrimp, or catfish, so they have more area to roam about in.

It comes as a blank glass tank only without any equipment. So, you will need to add your own lid, filter, heater, lighting, etc., depending on what you decide to house in it.

GloFish Aquarium Kit Fish Tank

This tank makes a great choice for any Glofish keeper. It is 20-gallons and comes with most extras needed to start a tropical freshwater set-up.

Included in this kit are a hood with LED lighting, Tetra Mini UL Heater, Tetra Whisper 20 filter, GloFish yellow anemone, 2 x plant multipacks, fish food, water conditioner sample, and a care guide. This offers amazing value; simply add substrate and livestock and you’re good to go!

The blue LED lighting that this tank provides looks amazing if you have Glofish within the tank; you can also purchase numerous GloFish accessories to jazz the aquarium up further if required.

This tank set-up is one of the better options if you’re wanting a complete set-up and intend to keep Glofish.

SeaClear Acrylic Aquarium Combo Set – Rectangle

This SeaClear aquarium is 20-gallon and made of high-quality acrylic. It comes as a blank tank with a hood and blue backdrop, and without other necessary supplies. It can be used for either freshwater or marine fish.

The clear acrylic top of the tank is pre-drilled with hoses for fitting the lid, a Hang-On-Back filter (not included), and a heater (not included).

The hood with its 15″ fluorescent light fixture is junk when most home aquariums these days use modern LED lights. However, there are no more available options to go for an acrylic aquarium with a medium volume of 20 gallons and you have to buy it if you prefer acrylic to glass.

I will show you the way to make it perfect with only small and easy customization. Just throw the lid away, then buy a 24-inch LED light fixture with extendable brackets and hang it on the acrylic top. Luckily, the top is flat to do so. It is also clear for light to penetrate through. Setting up in this way, the acrylic top will also protect the LED light fixture from damages from the aquarium water, and thus prolonging its lifespan.

SeaClear Acrylic Aquarium Combo Set – Hexagon

This 20-gallon aquarium is the same as the previous but it is a hexagonal one; for something that little bit different. It offers a unique shape and very clear viewing areas.

Like the previous, you will also make some customization for this tank to make it perfect. And you will need a 15-inch LED light fixture to fit on its top. You will also need to buy a filter and heater for setting it up. You can find these in the following sections in this article.

Tetra ColorFusion Aquarium

This 20-gallon tank is a beautiful complete set-up that would make an ideal first tank or a second smaller tank.

Scratch-resistant glass is used here, and the tank itself comes with a lifetime warranty. Also included are an LED hood, Tetra Whisper filter, Tetra HT 20 heater, water conditioner sample, digital thermometer, fishnet, care guide, and some decorations. You have everything ready to go, simply add your choice of substrate.

The special feature of this product is its color fusion LED lighting. It allows you to opt from several color choices, each designed to show off the best colors of the fish housed within the tank. This is one of the best options for those looking for a 20-gallon tank combo.

Landen Rimless Low Iron Aquarium Tank

This tank is slightly under 20-gallons, it will hold 17.1 gallons, and is constructed from heavy-duty 6mm glass. This glass is low-iron and offers very clear viewing. This is an ideal purchase for those who are finding a rimless tank to build an attractive planted aquascape.

If you’re looking for a basic tank that you can customize as you prefer; with your heater, lighting, etc. then this is one of the best options available. You get a strong, sturdy tank that you can set up exactly as you wish to.

SC Aquariums 24 Gallon All in One Reef Aquarium

This tank is slightly larger than most on the list and will hold 24 gallons. The aquarium is made from Starfire/low iron glass, which makes for beautiful transparency for viewing.

Three behind compartmentsThree behind compartments

It is specially designed with a built-in rear chamber overflow with three compartments for housing filter materials, a pump, and other equipment. This design hides all equipment from view leaving the tank with nothing more than an attractive aquascape with colorful fish.

The way it works is so easy to imagine; the pump pumps the water from the rear chamber to the main view tank, the overflow water from the main tank flows to the chamber containing filter materials through its drilled hoses for continuous filtration, and then returns to the tank with the pump.

You can use it for either a marine or freshwater setup. However, most aquarists built it as a nano reef because the back panel provides an ideal place to install a small protein skimmer. You will need to buy a reef tank LED light to fulfill the setup. I strongly recommend the Nicrew HyperReef 50 for the tank.

Featured 20-gallon aquarium accessories

Most twenty-gallon tanks will be sized as follows, give or take a small amount; for standard shaped tanks (24″ x 12.5″ x 16.5″) and long shaped tanks (30″ x 12.5″ x 12.5″) and will weigh around 220 lbs when filled. This allows you some ideas of what equipment can fit into the tanks.

20-gallon aquarium lid

Not all aquariums come with lids as standard so you may need to add one. To find the best one for your tank, ensure you measure up correctly and check against the dimensions of the lid you intend to buy.

20-gallon tank stand

Most 20-gallon aquariums do not come with a stand and it is advisable to use an aquarium stand as these are designed to hold the weight of the tank when filled with water. To choose the best stand you’d like then ensure the length and width of the tank itself match the stand and that the stand is suitable for holding the required weight.

Aquarium background

Many people like to use an aquarium background in their tanks, it adds imagery and depth to an aquarium and there’s an abundance of patterns and pictures to choose from.

To select the correct one, ensure you measure the total length and height of the tank and match it to the background you purchase. It is advisable to purchase a little bigger if you can not find the correct size, you can always trim it (carefully) to fit.

Lighting for 20-gallon tank

Most aquariums do come with lighting but if yours does not, or you wish to change the lighting unit to something different then you need to make sure that you choose a light that is suited to your aquarium.

You should make sure that the light is suitable for the length of your tank, and whether it is suited to plants and/or corals if you keep either of those. Not all lights are a fit-all solution and some are more specialized than others. You will need a 24-inch LED aquarium light for a 20-gallon high or a 30-inch LED aquarium light for a 20-gallon long.

20-gallon tank filters

Filtration is the most important thing to get correct when keeping an aquarium, they help to keep your water in peak condition for any livestock you keep.

When choosing a filter, you need to get one that is capable of turning over the volume of water in your tank 4 times per hour. That means in a 20-gallon aquarium you need one that turns over 80 GPH (gallons per hour).

100-watt heaters

If you intend on keeping tropical fish then a heater is a must-have item in the tank. Not all aquarium setups come with one included. If you’d like to add one then you need to ensure the one you put in the tank is suited to its size and can hold the temperature required.

As a basic rule of thumb, 1W is required per liter of water (or 3.8W/Gal), so for a 20-gallon tank, we’d advise a heater that is 75-100 watts.

Air pump

Uniclife Adjustable Air Pump 2 L/minUniclife Adjustable Air Pump 2 L/min

An air pump isn’t a necessity in an aquarium with filtration but many people opt to include one, or more, within their tanks. Air pumps are usually used to operate some action aquarium decorations and air-driven filters such as undergravel, sponge, and corner box filters.

The benefit of an air pump is that it creates water agitation, which in turn provides more oxygen to the aquarium water which is beneficial to livestock within.

For a 20-gallon aquarium, you need to look for one that has a minimum output of 0.660 liters/min. This also depends on how much equipment needs to be powered with the air pump and how deep your tank is.

If you keep a marine aquarium you will need a stronger one, owing to the fact saltwater has 20% less oxygen solubility than freshwater.

Water pump

A water pump is a great addition to an aquarium to create a flow within the tank. This helps to keep water fresh and also some fish benefit from stronger flows which they enjoy swimming in. You can also use a water pump to help with water changes.

When looking for a water pump you should get one that rotates the volume of water in your tank 5 times per hour. This means for a 20-gallon tank you’d need a minimum rate of 100GPH to ensure the best efficiency.

Decoration ideas

There are so many decoration options when it comes to an aquarium. You can have ornamental ones; from sunken ships, bridges, mountains, etc. to artificial plants, driftwood, caves. You should consider the fish you intend to keep when planning your décor as some prefer having hiding spots so you can match their needs to your preference for décor.

Fish compatibility & stocking ideas

Freshwater fish & inverts

If you decide to keep freshwater fish in your 20-gallon aquarium then you have quite a few options in what you can have. Here are a few of the better options to keep. Always refer to a stocking guide to ensure you don’t add too many fish to the tank.

Panda Corydoras


These Corydoras are far smaller than other species, which means they’re an option to keep them in a smaller aquarium. Cory’s tend to stay to the bottom of the tank the majority of the time and prefer to be in groups of 6 minimum. They grow to 1.75-2 inches so you can keep 6 within a 20-gallon tank. They’re amazing to watch and breed easily, when happy. They lay eggs usually on the aquarium glass or leaves of plants (if available in the tank).

Harlequin Rasbora


These are beautiful, striking fish that will add color to any tank. They grow to 2 inches maximum and are happiest in groups of 6-8. Harlequin Rasboras are suited to beginner keepers and feature a silver/orange body with a black triangular shape on their sides. These are best kept in a community setting, with other docile species of fish.

German Blue Ram


If you want a bold feature fish then the German Blue Ram is the fish for you! The females of the species have a pink belly and blue patches in a black spot on their sides; the males are similar but without the blue patches of color within the black spot.

If you decide to keep these fish then you can house 1 male with either 1 or 2 females if you have a 20-gallon tank. They do require higher temperatures than some community fish so ensure you match them with other fish that prefer warmer water.

Leopard Danio


Leopard Danios are lively small fish that prefer to swim at the top levels of a tank. They’re best kept in groups of 6 and are incredibly active. These are very hardy and can tolerate a wider parameter of pH, hardness, and water temperature, making them the perfect starter fish. They’re best kept with other active fish, to ensure that everyone has a chance to eat at feeding time.

Apistogramma dwarf cichlid


Apistogramma is a species of dwarf cichlid that is very colorful. They prefer to swim in the lower levels of a tank and prefer warmer temperatures, as most cichlids do. These will breed if paired and caves are provided and they care for their fry incredibly well. There a few varieties of Apistogramma but they are ideal if you’d prefer a cichlid tank and only have a smaller one available.

Pseudomugil Gertrudae rainbowfish


This is a small rainbowfish that is striking. It features a bright yellow body, blue eyes, and spotted fins. They may not be commonly available, depending on your location, but if you can get some then they make a fantastic addition to a community tank. Best kept in groups of 6+; if you have both males and females, you’ll see them display their colorful fins in an attempt to breed.



This fish grows to about 3 inches and is another great choice if you prefer cichlids. They are known for their fantastic swimming displays; they swim sideways, upside down, and even vertically to feel safe and protected and able to dart into a hiding spot. In a 20-gallon tank, you can keep 3-6 of these and they do prefer a tank with plenty of cover. Unlike a lot of cichlids, these are relatively peaceful and can be housed with other community fish.

Saltwater fish

If you wish to keep saltwater / marine fish within your 20-gallon aquarium there are several interesting species you can choose from. A 20-gallon tank is ideally sized for a nano marine setup. Here are a few fish you can choose from.



We have to start with the classic marine fish, this is one of the most popular choices for a marine tank and it is suitable for smaller tanks. There are numerous species of clownfish, most of which are fine for a 20-gallon tank. Most clownfish will get on fine with other tankmates but some species are a little more feisty.

An anemone is usually thought to be a must-have when keeping clownfish but they can do fine without one if you’re restricted on space to keep one.

Yellowtail Damsel

fish of the Indo-Pacific Coral Reef Ecosystem National Museum of Natural History. Fish species: Pomacentrus trichourus Yellowtail Damselfish Can be seen chasing other fish as it aggressively defends its territory. Photo by:Carl C. Hansen Neg # 96-10745

Image by Carl Malamud

This is a small fish that is happy both in schools and alone. They feature a bright blue body with a vivid yellow tail, hence their name. They are one of the more peaceful species of damselfish and can be kept with other marine fish, as long as they are not too aggressive.

Pajama Cardinalfish


This is a beautiful, peaceful fish that is perfect for a 20-gallon tank. They grow to around 2″ and you can keep one in this size tank. It is a slow-moving fish so must be kept with other non-aggressive fish. They do best with lots of cover and places to hide. You can keep these with corals safely.

Watchman Goby


Image by Haplochromis

This is a most unique fish, they’re peaceful with other fish except for other Goby’s (unless in a mated pair), so you should only keep 1 of these in a small saltwater tank. These grow to 3-4″ and need a sand substrate so that they can dig happily. They enjoy the company of Pistol Shrimp so they would make ideal tankmates.

Bangaii Cardinalfish


This cardinalfish is similar to the Pajama one, it is a peaceful species that can be kept with other non-aggressive fish. They grow to 2-3″ and you can house 1 in a 20-gallon tank. Bangaii Cardinalfish prefer to have rock in the aquarium that they can hide within. This species will also commonly breed, if in a pair, which is something fun to watch.

Royal Gamma Basslet


Image by Brian Gratwicke

This is a beautifully colored fish, with a mix of bright purple and yellow. They’re ideal for beginners, easy to care for, and quite hardy. It will grow to around 3″ and like places to hide in, so rocks and caves are required. They may take a shine to any small invertebrate in your tank so it’s best not to mix the two species.

Purple Firefish


Image from Wikipedia

This is sometimes known as a Purple dartfish, due to its shape. They’re thin and colorful and very fun to watch as they’re quite lively and active. It is a very peaceful fish and can be housed with most other peaceful species. They can grow to 3-4″ and like plenty of places to hide in a tank so rock formations are advised. The fish are known for jumping so please ensure you have a well-fitting lid on your tank.

How many fish can I keep in 20 gallons?

The amount of fish you can keep depends on the size of your tank and the size of the fish you keep.

In a freshwater tank, you can keep 1 inch of fish per gallon, based on the size of the fish when fully grown. E.g. You can keep 20 fish that maxes at 1 inch when fully grown.

In a marine tank, you can keep 4-5 fish, as long as these grow to 2-3″ maximum, if you have smaller species then you can add 1 or 2 more.

Setup and stocking ideas

There are so many options when it comes to aquascaping and this depends on the style you’re aiming for. But what is aquascaping? This is the art of laying out aquariums with hardscapes such as rocks, stones, wood, and plants. There are a few common styles and we’ll cover some options for you.

20 gallon planted aquarium


If you have a 20 gallon planted aquarium then a natural aquascape makes sense. This uses the plants within your tank to create a natural scape that resembles a natural landscape. You can use rocks and wood that you can plant on to build up the scape to look more realistic. Moss is your best friend when it comes to this style of scaping.

If you’d like a planted tank then how many can you have? Well, there’s no hard and fast rule for this, you can keep as many plants as you can fit as long as you have space for fish to swim around and have the lighting correct. Too many plants require more care, but if you have the time to maintain these then you can have as many as you see fit.

In a 20-gallon planted tank, you have so many options in terms of creating a small community tank, you can have a school of Harlequin Rasboras (6) or Neon Tetras and a few smaller shrimps that will create an active and colorful tank.

Fish-only aquarium without plants


If you want to make your decorations as the central piece of the aquascape, you may set up your tank in this kind. It is easy to maintain and clean with a tank without live plants. You don’t have to trim your plants and remove dead leaves weekly. Cleaning the gravel is much easier without any obstructive plants.

The best aquascaping for a fish-only tank is to use hardscaping materials only; gravel, rock, wood, plastic plants, and decorations work best in this instance. You can balance the colors and textures with any ornamental decorations you may have within the tank. This will allow you to create a landscape that is natural-looking without greenery.

Some live plants such as Marimo Moss Balls, Anubias, and Echinodorus can be added to supplement a little real green to the tank. These plants are low-demanding, slow-growing, and very easy to maintain.

20-gallon shrimp tank with/without live plants


Shrimp do enjoy hiding places so many aquascaping options would work here. The best options for aquascaping a shrimp tank will include caves, wood, and plants which are everything most shrimp love. Utilize the materials to create natural hiding holes for them which look like they are part of the landscape rather than a cave sat in the middle of the floor.

Find the detailed page for shrimp here: https://portlandaquarium.net/freshwater-shrimp/

20-gallon coldwater tank (unheated tank)


Zebra Danio tank

To aquascape a cold-water tank it is best done without using plants, rocks and stones work best in these tanks. You can build up natural towers, bridges, and caves to create stunning scenery that looks like it may belong in the stone ages. You are only limited by your imagination, even when restricted with your materials.

Make sure you keep all coldwater fish such as Zebra Danios (64° – 79° F) in the tank. Some other species for a 20-gallon coldwater tank include White Cloud Mountain Minnow (64° – 72° F), Clown Killifish (68° – 79° F), Hillstream Loach (65° – 77° F), Rainbow Shiner (50° – 72° F), Endler Guppies (66° – 84° F).

Common Guppies are tropical fish and don’t do well in coldwater that makes them easy to get diseases. If you have Guppies in a coldwater tank, ensure the temperature doesn’t drop below 68 °F (20 °C).

Saltwater fish-only with liverock (FOWLR)

If marine is your aquarium of choice then you can add a lot of color to your 20-gallon tank. You can have a clownfish, with a yellowtail damselfish, a royal gamma basslet, and a purple firefish. That gives you a wide variety of colors and activity levels and will make a striking little marine setup.

You can aquascape a marine tank with liverock fairly easily, you can use the rock within to create structures and natural-forming hidden holes for your fish. You need to ensure however that everything is not stacked or put together too tightly, to make for easy clean-up of food waste, etc. Liverock is relatively easy to stack up, to gain height within the scape.

20- gallon reef aquarium


Your imagination is your best friend when scaping a reef tank, imagine the reefs that are natural out at sea and aim to create a miniature version. You can mix colors and shapes to recreate a natural-looking formation. Do not worry about perfection when doing a reef scape as it is not perfect out in the deep blue sea. Random reefs placed strategically work best in this setup.

20-gallon species aquariums

You can keep one or two species with the closed water conditions in the same tank. It could be a community Tetra tank with different types of Tetra, livebearer tank with Guppies and Platies, Rasbora tank,…


Dwarf Puffer tank

This kind of aquariums is also suitable for some specific species, which are aggressive to other fish, such as Eyespot Puffers, Dwarf Pea Puffers, Dwarf cichlids, Dwarf Gouramis, Bettas, etc.

If you wish to aquascape a species tank then you need to fit the scaping in with the fish you keep.

If you prefer a cichlid tank you can keep 2 German Blue Rams (1 male and 1 female recommended) with an Apistogramma and some shrimp that prefer warmer water.

If you have a Betta tank, they enjoy resting places, that can be easily added and combined with your overall scaping look. You can keep multiple male Bettas in a 20-gallon tank with the help of dividers. You can use those dividers to help create individual aquascapes that are visually pleasing.

20-gallon aquaponics fish tank

ECO-Cycle Aquaponics Indoor Garden SystemECO-Cycle Aquaponics Indoor Garden System

If you own an Aquaponics tank then you can scape this in a natural way, which will best show off its unique planting system within. You will need a 20-gallon aquaponics kit to build your tank this way.

It is a self-sufficient tank and already has a natural look, due to the plants that grow above it. This will look stunning with a green planted floor and a few rocks placed around, for a natural aquascape.

Setting up a 20-gallon aquarium


Setting up a 20-gallon aquarium is relatively simple, you need the basics – substrate, lights, heater (if keeping tropical fish), filter, and livestock. That is the bare minimum equipment you need to get going. Most aquariums come with everything needed to get going, except for the substrate.

How much substrate will you need? A pound per gallon is a good rule-of-thumb and you need this to be 2-3 inches deep if you intend to have live plants within it.

To set your aquarium up you should follow these steps:

  1. Choose location – you need to ensure you have a location ready for the tank, it needs to be near electrical sockets, away from windows and near the location you do water changes from.
  2. Place on the stand – ensure the tank fits on the stand properly before adding anything to the tank. Make sure everything is level and you’re completely happy with its position.
  3. Add filter – add your media, or cartridge, to the filter and check that the filter will fit where it will be positioned in the tank.
  4. Electrics – ensure the electrical outlets are safe to use, that all wires have drip-loops and that any extension cord has a breaker.
  5. Aquascape – the fun part! Add substrate and any other materials (wood/rock) and scape to your liking. Always fully rinse the substrate, until the water runs clear.
  6. Fill up – add water and water conditioner to the tank. Do this slowly to ensure your scaping hard work is not destroyed. Once full you can run the filter to ensure this is working.
  7. Lighting – switch on the lights, check all bulbs are working and are a safe distance from any water.
  8. Cycle – the most important step of setup is ensuring the tank is fully cycled and ready before adding any livestock. A fishless cycle (using ammonia) is the best way to do this.
  9. Add fish – only do this once the tank is fully cycled and shows 0 ammonia and nitrites.

Read the detailed page: https://portlandaquarium.net/freshwater-aquarium-setup/

How to clean a 20-gallon aquarium

Cleaning an aquarium should be part of your routine and is fairly easy to do. You can use tools for this job. If you have a planted tank then you can cut back these when needed and remove plant waste from the floor with pincers/tweezers.

You can remove food waste by using a gravel vacuum which is ideal for cleaning substrate. Most aquarium keepers tie in their cleaning schedule with their water changes so that they are not disturbing the fish more than needed.

Lucas has keeping successful fish, planted, and reef tanks for many years. He loves to collect aquatic organisms and have as many aquariums as he can afford.

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