10 vs 20 Gallon Fish Tanks – Which is Best for Your?

For decades, adept aquarists have hailed the 20-gallon tanks for several reasons. They attribute the tank to an ideal size sufficient when starting-out.

Most of the tanks in this category also come with additional accessories such as filters, lighting systems and heaters that are necesary for better fish keeping.

10 vs 20 Gallon Fish Tanks

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10 vs 20 Gallon Fish Tanks

However, down the line, 20-gallon tanks are facing stiff competition from their 10-gallon counterparts. You will often hear skilled aquarists talk of 10-gallon as an ideal substitute for 20-gallon tank.

How true is this notion? Stay tuned as we take you through every iota of information you need to know when enlisting your options.

Weight and Size

Your tank’s weight and size matters a lot. They give insights on where on the number of pets you should place in the tank. They also help in choosing the ideal spot in your homestead that is secure and comfortable enough to accommodate your tank.

A 20-gallon tank is the standard aquarium tank used by most aquarists around the world. It comes as either 20-gallon high or 20-gallon long. A twenty-gallon high measures 24 x 12 x 16 inches and weighs 25 when empty. When full with water and other accessories, the tank weighs approximately 225 lbs.

20-gallon high measures 30 x 12 x 20 inches; and weighs 25 lbs, 225 lbs when empty, and full respectively. However, it is worth noting that glass tanks are heavier as compared to acrylic. The weight of the glass tank of the same size is 3 to 4 times that of a glass tank. However, the type of plants and filters you put inside your tank plays a huge role in defining the overall weight.

On the other hand, a 10-gallon tank comes in only one standard size; 10-gallon leader. This aquarium measures 20 X 10X 12 inches in size. It weighs 11 lbs and 62 lbs when empty and full respectively. Just like the 20-gallon tank, a glass tank of the same measurement weighs 3 to 4 times that of acrylic materiality.

It is prudent to know that these weights may slightly vary with some slight margins. This is due to the density of your aquarium water, the weight of the apparatus inside and other debris.

A 20-gallon tank provides an adequate space where your pets can swim without any notable hindrances that come with limited space. The number of pets you are adopting should help you choose between the two variants. However, the spacious the better.

On other, you may find that you lack an adequate hosting room for a large tank. Due to its extra weight, a 20-gallon tank needs something sturdy enough. Additionally, these tanks are heavier. You may not be able to relocate them painlessly from one room to another without emptying. Therefore, if you are looking for something navigable, a 10-gallon tank is the ideal option to go for.

Fist Tank Maintenance

The bulk of domestic fish keeping lies in maintenance. Acquiring a new tank is just but the beginning. And, the size of your tank determines the overall pain or buzz in maintaining your pet.

When keeping your fish, there are some maintenance rules that you must abide by. You should change approximately 25% of your aquarium water every three to four weeks.  During this process, you do not necessarily need to remove the fish from the water. Secondly, your water temperature should be ideal for species of fish you are keeping.

Most fish species thrive in a temperature range between 76 to 80 degrees Fahrenheit (25 to 27 degrees Celsius). This is the average temperature requirement for tropical species. Cold-water species of fish require a slightly lower temperature. They thrive better in a range between 60 to 75degrees Fahrenheit (15-24 degrees Celsius)

Just like humans, your aquarium fish needs oxygen to survive. When you open your aquarium lid, oxygen infiltrates through osmosis inside your tank. When your water temperature is warmer, this process of infiltration is greatly hindered hence resulting in lower concentrations of oxygen.

In slightly low temperatures such as during winters, the tank water will freeze. This also impairs infiltration of oxygen inside. To avoid waking up to a suffocated and floating fish, you must ensure that your aquarium temperature remains within range.

Lastly, the pH and ammonia concentrations in your aquarium must also be within range. First, your aquarium should not hoard any ammonia content. It should have zero content of ammonia for a conducive survival environment.

The phosphate, Nitrite and ammonia contents in the aquarium, always result in pH fluctuations. An ideal pH should range from 6-8. Most aquarium species cannot tolerate frequent changes in pH. Anything below this range will automatically affect the health of your fish.

10 Gallon or 20 Gallon Fish Tank? Which to Choose?

To juggle between all these requirements, you must keep an eagle’s eye on the type and size of the aquarium tank before making any purchase.

10-Gallon Tank

A 10-gallon tank is one of the ideal sizes when starting. They are not too big and also very easy to navigate in the room. However, based on the size factors, it may not be easy to maintain.

When working with this size of a tank, you must first determine the ideal number of fish to acquire. Some simple logic applies when choosing your number. Consider working with a gallon of water for every small fish—adding the fish in small groups for some weeks.

However, do not leave the fish to outgrow your tank. You may need a bigger tank for your growing fish. However, when enlisting your options, take into consideration the adult size of the pets and not their current sizes.

In the course of your journey, you will realize that the tank comes with sundry of limitations. One, a ten-gallon tank may not be spacious enough for more aggressive fish. It may not be near the requirements for best swimmer species of fish.

Secondly, a 10-gallon tank may not be able to accommodate most of the desired aquarium plants. Your pets may lack ideal hideouts. And thirdly, waste accumulation is a frequent barrier to proper maintenance. Some species produce a lot of waste. Meaning, even with a low number of occupants, your tank’s water parameters may still go out of control hence resulting in death.

20-Gallon Tank

20-gallon is a standard size. The tank comes with numerous benefits when it comes to maintenance of the aquarium fish.

First, a 20-gallon tank provides extra spaces for swimming and accommodation of other aquarium accessories. You can implant your favourite aquarium plants in the tank without suffocating your fish. Secondly, a 20-gallon tank holds more water.

Wastes generated from food remains and biological excretions from the fish will not cause notable fluctuations in the water parameters. With an appropriate number of occupants, you will effortlessly maintain your aquarium without incurring much in the form of energy and money.

Fish Species for 10 Gallon Tanks

Not all fish species are ideal for small tanks. Some of the few reasons why your 10-gallon tank may not be the best include;

  • The overgrown size of adult fish
  • Waste generation
  • Aggressiveness

The following species of fish thrive well in a 10-gallon tank:


Two male betta splendens are a better choice for a 10-gallon tank. These species of fish grow to a maximum of 2.5 inches adult length. They are great swimmers and fancy hideouts in a cool environment.

One male beta thrives well in any confined environment. However, they are compatible with other species in a community tank. Otherwise, you need to take your time to understand the behavior of these fish.


Fancy guppies are another ideal option for a 10-gallon tank. Biologically, the sizes of guppies vary much.  Male guppies feature a size range between 0.6-1.4 inches in length.

Female counterparts feature a size range between 1.2-2.4 inches long.

Dwarf Gourami

Dwarf Gourami survives better in low oxygen concentration areas. Just like bettas, they are anabantid species meaning they can breathe even air that is above water level.

Dwarf gourami grows to a maximum of 3 inches adult lengths. Your 10-gallon tank can comfortably accommodate 2 dwarfs without any hindrance.

Zebra Danios

Zebra danio fits almost all tank size. For a 10-gallon tank, you can stock these species of fish in a school of five or six. Unlike other types of fish species mentioned, Danios are hardier. They can easily survive even extreme aquarium parameters.

Fish Species for 20 Gallon Tanks

A 20-gallon tank can accommodate any popular species of aquarium fish (check out my other article about ideas on how to stock a 20 gallon tank). Some of the popular species that works best for this size tank include:

  • Swordtails
  • Platty Fish
  • Molly fish
  • Cory catfish
  • And all the aforementioned species above.


Choosing your right size tank goes beyond the difference between a 10-gallon and a 20-gallon tank. It entails choosing the correct apparatus that are cardinal for fish keeping. Many aquarium kits come with pre-installed or easy-to-install heaters, filters and other accessories.

On the other hand, 10-gallon and other nano tanks demand separate installation of these accessories. This can inconvenience you more so when green on how to choose ideal equipment. Otherwise, the type and number of fish you need to play a huge role when it comes to choosing between the two variants.

Questions and Answers

Tom Clark March 8, 2020 Reply

I just read here that you recommend changing water every 3 to 4 weeks. Everyone else I have seen says every week.Please explain this. I am not implying that you are wrong, I just don’t understand why. Neither do I understand why they say one inch of fish requires one gallon of water, a rule that none of them seem to follow.It all depends on the type of fish, size of tank, and how well the tank is cared for.I am an amateur with 45 days experience and all these so called pros are very confusing, making a simple hobby so complicated.I finally learned to stick with you and Jason and ignore the rest, now I am enjoying my little hobby.Thank you so much Fabian for your site.

    Hey Tom, thanks for your input!
    The one inch fish / gallon rule is very general; this gives beginners the opportunity to calculate how many fish they can place in a tank. I always advice beginners to start with less fish and try to learn the hobby first, and then increase the number of fish as they gain more experience. I know, that there is a lot of information out there, and it might be confusing, especially if you new to the hobby.
    In new tanks, you should do water changes weekly. In established aquariums, with really good filtration, great amount of live vegetation and not too many fish, it is enough to change water once a month, or do just top-ups.
    For instance, I have larger (55+ gallon) tanks, where I only add water to the tank, but don’t change the water. I have lots of fast growing plants (Elodea and Frogbits), and don’t have too many fish.
    There are many things in this hobby that will work for one but won’t work for others. So it is good, that you follow a general rule, but it is best that overtime you develop your own schedule.

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