Best 20 Gallon Fish Tank: Top 5 Easy-To-Customize Options

best 20-gallon fish tank
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Last Updated: August 30, 2023 by Flora Gibbins

I am still in shock after seeing my neighbor’s new Fantail goldfish swimming around in an oversized sherry glass. My decades of aquarium care experience were about to help rescue this precious little fish.

Here’s the deal…

Most aquarium fish live longest in a 20-gallon aquarium. And to me, the best 20-gallon fish tank is the Perfecto All Glass Aquarium Tank because it’s very easy to customize. I’ll tell you more about that in a while, so keep on reading.

Still, a bare-bones tank may be intimidating to a new aquarium keeper. This is why I helped my neighbor shop for the best 20-gallon fish tank kit instead.

The 5 Best 20 Gallon Aquariums Reviewed

1. Perfecto All Glass Aquarium Tank – Best Overall

There is a saying that the best 20-gallon fish tank is the one you can afford. That includes the cost of vital accessories like the filter, heater, and hood.

In their wild habitats, different species of fish are accustomed to different water types. It’s not just about the pH and hardness. Water suitability is also about the rate of flow and where that flow originates.

For example, Angel Fish are accustomed to very slow-moving water. Tiger barbs, on the other hand, tend to live in medium to fast-moving streams.

If you put tiger barbs in a tank with slow water motion, they will be more inclined to develop gill infections and disease.

This is why being able to customize your tank’s filtration and water flow speed is very important. With the Perfecto All Glass Aquarium, you have the best opportunity to buy the right filter for the fish you are interested in keeping. 

In the long run, this saves you money and also helps ensure your aquatic pets remain as happy and healthy as possible.


  • Standard 20-gallon tank dimensions make finding accessories easy 
  • Plenty of budget-friendly options for filters, decorations, lighting, and heaters
  • Limitless optimization potential lets you change accessories as you learn


  • Lack of even a basic screen hood means fish can jump out of the tank
  • Limitless options can make it hard for beginners to get it up and running quickly


Since your interest in fish species may change over time, the accessories will also change. No matter whether you need a gentle bubble filter, or more robust water movement, the Perfecto All Glass Aquarium Tank will suit your needs.


2. Marina LED Aquarium Kit – Best Kit for Biofilter Preservation

The Marina LED Aquarium Kit is unique among other 20-gallon aquarium kits in the sense that it comes with a filter that lets you change just 25% of the filter media at a time.

Aside from the tank itself, the filter is the most important thing to keeping your fish happy and healthy.

The filter doesn’t just remove debris from the water. The media within the filter acts as a home for billions of bacteria that break down ammonia and other fish waste.

Without these bacteria, your fish could not live in the tank for more than a few hours. This is why having a filter that allows you to stagger changes in the media is so important.

This is one of the best 20-gallon aquariums for beginners interested in keeping smaller coldwater fish like Fantails, Ryukin, or Butterfly Goldfish. 

Since these fish can produce a lot of waste, being able to stagger filter media changes is essential to good health and good water quality.


  • Comes with a filter that prevents loss of biofilter with media change
  • Best 20-gallon aquarium starter if you have a tight budget
  • Hood is tight-fitting and sturdy, making it ideal for nervous fish or jumpers


  • LED light array is exposed to condensation and water from inside the tank 
  • Hood only has cutouts for the filter and a feeding hole
  • Lack of hood cutouts makes it hard to add heaters and other accessories


If you are on a tight budget and don’t know which filter to start with, the Marina LED Aquarium Kit will suit your needs. This kit will enable you to build a healthy community tank for coldwater fish and others that don’t require a heater.


3. GloFish Aquarium Kit – Best Tank Kit for Beginners

I got started in aquarium keeping when I saw the cutest little tiger barbs swimming around in a department store tank.  Back then, there was no internet, let alone a 20-gallon fish tank review to help me figure out what these fish needed.

No one told me that I needed a school of at least 6 tiger barbs to avoid the fish version of social chaos.  Nor did anyone tell me these tiny little fish needed something bigger than a goldfish bowl to live in.

Within a few days, I wound up buying a 10-gallon tank and frantically trying to figure out how I was going to keep those fish alive while the tank completed its first nitrogen cycle.

The GloFish Aquarium Kit Fish Tank with LED Lighting and Filtration Included is the most complete kit you will find. It is suitable if you spontaneously bought some fish and didn’t realize you need things like a conditioner to make tap water safe.

Since this tank also has plenty of customization space on the hood, you can easily add accessories as you learn.  This will help you save fish from all kinds of mistakes.


  • Comes with everything you need to start up a new tank from scratch
  • Can change accessories without having to buy a new hood or a new tank
  • Included heater makes it easy to convert from cold water to tropical fish


  • Plastic plants and mats may have sharp surfaces that injure the fish
  • Filter body has a tight-fitting media area that requires a single cartridge 
  • No way to preserve biofilter when you remove the filter cartridge


If you bought pet fish on the spur of the moment, this tank will get you through the initial learning curve. As you learn more about what you want in terms of accessories, you can easily customize the GloFish Aquarium Kit Fish Tank without a lot of problems.


4. Aqueon LED Starter Kit – Best Budget Tank for Tall Fish

Have you ever seen young Angel Fish with bodies that are barely the size of a quarter? When their fins are fully opened, they account for 2/3 of the fish’s total body height.

Unlike Tiger Barbs, Tetras, Guppies, and Fantails, the main body of an Angel Fish can easily grow 5+ inches in diameter. When their fins are fully extended, that means the fish can easily require 15 inches in depth of water just to swim in a straight line.

The nice thing about the Aqueon LED Aquarium Starter Kit is it has a height of 19.5 inches, which is a few inches taller than some of the other best 20-gallon fish tank kits. 

This makes it suitable for young to middle-aged Angel Fish and others with narrow, disk-shaped bodies or very tall fins.

Since this tank also has a bit more depth, it is also very useful for community tanks where you want to have a clear division between lower, mid, and upper dwelling fish.


  • Best budget option for a high-profile tank
  • Filter comes with a monitor that tells you when to change the media 
  • The feeding port comes with a cover 
  • Covered ports help prevent debris from outside from getting into the tank


  • LED light array is exposed to condensation which might be a hazard  
  • Filter cartridge cutout is located in the center of the hood, making it hard to access 
  • Poor hood access means you are more likely to disturb the fish when doing maintenance.  


The Aqueon LED Aquarium Starter Kit is one of the few beginner kits on the market that features a high-profile tank. This makes it a good starter tank if you plan to keep Angel Fish or a community of fish with well-defined regions of habitation.


5. LANDEN Clear Rimless Tank – Best Saltwater Starter Tank

LANDEN Ultra Clear Glass Rimless Low Iron Aquarium Tank

When I first got into aquarium keeping, saltwater tank owners usually didn’t settle for less than 250 gallons.  The fishes were almost exclusively wild-caught and had life insurance because they were so hard to obtain.

These days, it is entirely possible to start and maintain saltwater tropical fish in a 20-gallon setup like the Landen Ultra Clear Glass Rimless Low Iron Aquarium Tank.

At first glance, you may think this is just a really expensive bare-bones tank. After decades of tussling with filters that are too small or the wrong shape, I can safely say this tank is different.

Unlike other tanks, this one comes with plenty of spare room to customize the filtration.

You can do everything from adding a protein skimmer to keeping an extra compartment for experimenting with resins and other new media.

Regardless of the shape of the media, you will never need to worry about the inlet, outlet, and keeping it all in one place.

If your ultimate goal is keeping saltwater aquatic creatures, the Landen Rimless Aquarium Tank is an ideal choice. You can also use it just as easily for freshwater fish that may have special filtration needs.


  • Can be used for freshwater and saltwater habitats 
  • Very easy to customize filtration
  • A rimless design is very attractive and modern-looking.


  • Hard to find a hood that fits a rimless aquarium
  • Not budget-friendly if you are only planning to keep freshwater fish


The Landen Rimless is ideal if you are planning to get into saltwater fish care. It is also the ideal tank for advanced tropical and coldwater aquariums as it allows for very easy customization of filter media and other options.


Factors When Buying a 20 Gallon Aquarium

Acrylic Tanks vs Glass 20 Gallon Tanks

When it comes to smaller tanks, I always say go with acrylic if you can. First, these tanks don’t have any seams. Some are also curved, which makes for an interesting viewing experience.

Insofar as 20-gallon tanks, I tend to be unimpressed by the quality of the tanks on the market.

Many of these tanks will leak just as surely as a glass one. Others will bow or flex from the weight of the water in the tank pressing against the walls.

If you are still considering an acrylic aquarium, this video may help you get some ideas about how each material differs in terms of optics. It also gives some good examples of how each material responds to abrasives.

Make Sure the Tank Is on a Level Surface

One of the biggest killers of aquarium seams is uneven floors. Remember, each gallon of water weighs about 8 pounds. When the tank is not level, gravity pushes all that weight onto one, or at most two seams that aren’t built to take it.

Take Your Time Establishing the Nitrogen Cycle in the Tank

The more water you have in the tank, the longer it will take for the ammonia and nitrate surges to be managed by beneficial bacteria.

Just keep doing the water tests and be patient while the tank is cycling. Later on, when you introduce fish into the tank, they will settle in faster and do better.

Beware of Palytoxin

If you are planning to keep saltwater fish, there is a toxin that can build up in the tank that will make you very sick.

Palytoxin is produced by creatures that look similar to anemones. You will be at most risk from encountering the organisms that produce Palytoxin if you decide to pursue reef tanks. Before buying aquatic creatures, make sure they are certified free of hazardous organisms.

Frequently Asked Questions (FAQs)

Is a 20 Gallon fish tank good enough for getting started?

Unless you are planning to keep feeder goldfish (fish purchased to feed other animals) or other large-bodied fish, a 20-gallon tank will suit the needs of most fish.

tank with goldfish

How many fish should be in a 20 Gallon aquarium?

The general rule of thumb is 1 gallon of water for each inch of body length. I tend to disagree with this because the fish’s swimming habits and temperament are as important as water chemistry and filter load concerns.

First, each species of fish will be most comfortable at a specific depth in the tank. Some will rarely come to the top, while others will stay in the middle or top region.  

If you don’t allow for enough water in each of these regions for each fish,  it can lead to serious territorial problems.

Swimming speed is also important to consider.  For example, a feeder goldfish is every bit as healthy and as beautiful as fish that are sold as pets. They also grow very quickly and are active swimmers.

Unfortunately, goldfish can also be very skittish and will bash as hard as they can into tank walls during thunderstorms or when startled.

Even a goldfish that is only 3” long can bash itself hard enough to do serious internal injury and die in a 20 gallon tank.

While Tiger Barbs are tiny fish, they need a lot of room to swim and school. A tank that is too small can cause extreme stress and increased aggression. 

You can keep more tiger barbs in a 20 gallon tank than goldfish from a water quality perspective.

From a size and temperament perspective, the tank is too small for even one goldfish.  It’s just about right for a school of 6 – 12 tiger barbs as long as they aren’t housed with other fish that they might terrorize.

What is the biggest fish size you can put in a 20 Gallon fish tank?

This depends on whether the fish needs to be in a school, and how energetic the species is. I’d recommend keeping the adult fish size under 2.5” to ensure each fish has enough territory and also enough room to dart without getting injured.

If you are successful in keeping your fish for more than a year, many species will double in size or more.

Since moving fish from one tank to another can be difficult, it is best to buy a tank big enough to house all the adult-sized fish you intend to keep in the tank.


After many years, and aquariums, I conclude that the Perfecto All Glass Aquarium Tank is the best 20 gallon aquarium.

Choosing your accessories has many advantages over using a kit.

As you go through the process of establishing a robust nitrogen cycle, you will appreciate the ease of changing filter types and media as needed.

Since it’s made of glass, the Perfecto All Glass is easier to clean than an acrylic tank.

It is my sincere hope this 20 gallon fish tank review helps you find the best tank for your aquatic pet needs.

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