How Many Glofish Tetras Can You Keep in A 20 Gallon Tank?

Glofish are luminous, fast-swimming fish with rainbow-like bodies that liven up an aquarium. These bright tetras need a lot of space. If you think that Glofish, being small, can fit in any community tank, you might soon regret it. 

However, we recommend no more than 9 – 10 Glofish tetras in a 20-gallon tank. 

Considering the genetic 2-inch size of Glofish, let’s see how many you can fit into a 20-gallon tank.

Also Read: Boesemani Rainbowfish

How Many Gallons Do Glofish Tetras Need?

How Many Gallons Do Glofish Tetras Need
Source: Scott Hart

The one-inch per gallon rule does not apply to Glofish because their activity level demands more space. While they love tank decorations, Glofish also need extra space to move, so a small tank can’t be as planted or decorated. 

You need a 10-gallon tank to house a family of 5 tetras. But this leaves no room for plants or aquascaping. For a 20-gallon tank to house these 2-inch fish, you can only keep 9 – 10 Glofish tetras.

In the case of a long-fin tetra, you must consider its additional length. A long-finned Glofish grows up to 3 inches. In a 20-gallon tank, you can only keep 7 – 8 long-finned glofish tetras.

To house a small family of Glofish tetras, you will need a minimum of 20 gallons. Always choose a bigger tank size than you think you need.

Also check out How Many Glofish in 5-Gallon tank?

How Many GloFish Tetras Can You Keep Per Gallon?

In a 10-gallon tank, you can keep around 5 short-finned Glofish tetras or 3 long-finned Glofish tetras. If you have a 20-gallon tank, it’s best to stick to 8 short-finned Glofish or 5 long-finned Glofish. Longer tanks can accommodate more Glofish as they love to swim and move around freely in the tank.

For a 20-gallon tank, it’s not a case of doubling up. Instead, you need to round down, not up, as the fish require more swimming space if there are more of them. So, in a 20-gallon tank, you should only house 8 short-finned or 5 long-finned Glofish tetras. 

The dimensions of your tank will also influence the success and health of the number of Glofish you house. Longer tanks can accommodate more Glofish as they prefer to race horizontally in the tank, even doing laps with their school. 

The general one-inch per gallon rule only works for select fish species. The simple calculation results do not factor in the tank setup, substrate, hiding places like stones and coral, or plants.

Can Glofish Tetra be Alone?

Tetras are a very social species and quickly get depressed if isolated. They are schooling fish, just like Danios. If you have a school of Zebra danio and black skirt tetra, they will coordinate their movements with the Glofish and live peacefully together. You’ll see both the Danios and Tetras swimming in the same direction. This unity is very calming to watch.

If you do not keep Glofish in schools, they might suffer from depression and die.

How Does An Overpopulated Tank Affect Your Glofish Tetra?

Glofish need their space and community. However, if you overfill a small tank with Glofish Tetras and other fish species, it will end badly for your Glofish. What could happen because of an overpopulated tank is injuries or depression. 

If the fish feel uncomfortable, they will become depressed, and you will start noticing signs of ill health. Some signs are struggling to breathe, losing appetite, dull or faded color of the tetras, frayed fins, etc. All of these can occur as a result of an overpopulated tank. This is why we always recommend investing in a slightly bigger tank for your Glofish Tetra.

10 Best Recommended Glofish 20-Gallon Tank

1. Glofish Aquarium Kit- All-In-One

GloFish Aquarium Kit- All-In-One

This all-in-one kit includes all the essential equipment to set up your aquarium. It consists of a 20-gallon aquarium, one LED hood, one Tetra Mini UL heater, one Tetra Whisper-20 filter, one Glofish 13” LED light stick, three Glofish plants, and one Glofish yellow anemone. The only addition you will have to make is choosing and adding your substrate

If you are dipping your toes in keeping fish and do not know what products to buy, this tank will give you a good teaser of the available products.


  • Material: glass
  • Item dimensions: 27.88” x 16.13” x 20.38”
  • Weight: 34.4 pounds
  • Style: tank kit
  • Shape: Rectangular


  • Easy to set up and use
  • Glass tank
  • Includes an LED light kit, heater, and filter
  • Perfect for beginners


  • Lacks different size options for upgrade

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2. The Aqueon 20 Gallon High LED Beginner Aquarium Kit

The Aqueon 20 Gallon High LED Beginner Aquarium Kit

This tank is the best budget option in the 20-gallon tank category, and it comes packed with all the basics needed to set up your tank. It is more affordable compared to other 20-gallon kits, given the number of products that come with the tank. The kit also offers a 3-stage filter system – its unique selling point.


  • Material: Glass
  • Tank dimensions: 24 x 13 x 17 inches
  • Kit includes: One 20 gallon glass aquarium, an LED hood, filter cartridge, Quietflow Power filter, submersible preset heater, thermometer, and setup guide


  • Completely packed with necessities
  • Affordable
  • Good quality


  • The tank is not rimless
  • The heater quality is dubious

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3. Tetra Aquarium 20 Gallon Fish Tank Kit

Tetra Aquarium 20 Gallon Fish Tank Kit

Tetra is a renowned brand, and it delivers another great starter kit in this 20-gallon tank, complete with a filter, heater, LED hood, and more. Just add gravel and fish, and you’re ready to go. 

The scratch-resistant glass will ensure unobscured viewing pleasure for many years, and your Glofish can race each other across all 24.2 inches of tank length.


  • Tank dimensions: 24.2″ L x 12.4″ W x 16.7″ H
  • Includes LED hood, Tetra Mini UL heater, Tetra Whisper 20 filter, artificial plants


  • Easy to set up
  • It comes fully assembled; just hook the heater and filter in place
  • Clip hinges of the lid to the glass side of the tank
  • Affordably priced


  • The filter and heater aren’t the best quality

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4. Tetra Complete LED Aquarium 20 Gallons

Tetra Complete LED Aquarium 20 Gallons

Step up a little in quality with the next Tetra 20-gallon model tank. The lid has white LED lights fitted, while the filter comes with a large biobag. The heater has a thermometer to monitor water temperatures for a consistent environment for your Glofish. 

The kit even includes water conditioner samples and fish food too. You only need to add substrate, a few plants, and your 8 – 9 Glofish.  


  • Tank dimensions: 24” (W) x 16” (H) x 12” (deep)
  • Includes: tank, Tetra Whisper 20 filter, 100-watt heater, and thermometer, samples 


  • Ideal size for Glofish, with enough room to move
  • Filter comes with biobag, enabling better filtration 
  • Consistent water temperature is achieved with the thermometer and heater


  • The filter can be a bit noisy

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5. Landen 60P 26.23 Gallon Ultra Clear

Landen 60P 26.23 Gallon Ultra Clear

There are times when you want to have just a slightly bigger tank so you can add that lovely ghostship aerator you’ve been eyeing, and that’s when having a 26.23-gallon tank is ideal. The tank can accommodate your maximum number of Glofish tetra, plants, and tank decorations to allow enough room for your fish to move and enjoy the tank decorations. 

This tank includes a filtration chamber hidden at the back, a return pump, and an additional length tank, which is ideal for fast-swimming Glofish. 


  • Tank dimensions: 23.62” (L) × 17.72” (W) × 15.75” (H) 
  • Tank capacity: 26.23 gallons (including sump area)
  • Actual tank size: 20 gallons


  • Tank includes filtration chambers, configured according to your filtration needs, and a powerful return pump
  • Hidden filtration chambers leave the main tank space unspoiled for the fish to enjoy 


  • Somewhat pricey, and you’d need to buy a heater too.

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6. Lifegard Aquatics 20 Gallon Rimless Clear Glass Aquarium

Lifegard Aquatics 20 Gallon Rimless Clear Glass Aquarium

Perhaps you’re upscaling and just want a larger capacity tank? Then the Lifegard 20-gallon tank might be perfect for you. This is a tank-only purchase, but you’re getting an excellent quality tank made from the highest quality glass, with German precision aquatic silicone to secure all joints. 

Adding the high-density foam mat is a nice touch, helping to level the tank when you install it. 


  • Tank dimensions: 24.4” x 12.2” x 15.74”
  • Capacity: 20 gallons


  • The tank provides a blank slate to play with, and you can add your own tank fittings and decorations as you like
  • Good price 
  • The self-leveling foam mat is ideal for a neat finish


  • You would still need to add your own tank equipment, which can cost you much more

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7. Fluval Flex Aquarium Kit, Black, 15 Gallon

Fluval Flex Aquarium Kit, Black, 15 Gallon

Okay, so a 20-gallon tank may be too big for your home, in which case, you can scale down slightly to a 15-gallon tank—ideally appointed for Glofish. The Fluval Flex is ideal for your glowing fish to enjoy, despite being somewhat smaller than a larger 20-gallon tank. 

The longer length dimension and the curved front panel of the tank give more space for your Glofish to romp around. 


  • Tank dimensions: 15.94” x 16.73” x 15.94”
  • Features hidden filter chamber
  • Includes filtration media
  • Versatile lighting kit 


  • The longer length tank is ideal for tetras to swim laps
  • Well-priced
  • Advanced lighting kit with special features to choose from


  • The return pump isn’t the best quality

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8. SeaClear 20 Gal Acrylic Aquarium Combo Set with LED Lighting

SeaClear 20 Gal Acrylic Aquarium Combo Set with LED Lighting

Since Glofish love swimming, a lean and long tank is ideal, making the SeaClear 20-gallon tank a winner. The tank dimensions are ideally suited to tetras. The expanding light is another great addition. 


  • Tank dimensions: 24” x 13” x 16”
  • Acrylic material
  • Black or blue backing
  • Includes expanding lighting set


  • The extra length of 24 inches is ideal for your fish
  • Good quality lighting kit, which expands
  • The acrylic material of the tank is ultra clear for viewing pleasure
  • Curved corners create uninterrupted views


  •  Very expensive, especially considering that the tank doesn’t include filters or heaters

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9. Midwest Tropical Fountain 25 Gallon Aqua Coffee Table Aquarium Tank

Midwest Tropical Fountain 25 Gallon Aqua Coffee Table Aquarium Tank

If you want something extraordinary and have the budget, then the Midwest Tropical Fountain coffee table is it! View your Glofish races from a bird’s eye view thanks to this unique tank system. 

The table has a built-in tank, which has a unique filtration base.


  • Tank dimensions: 25” x 27.5” x 28”
  • Made of glass and acrylic 


  • Submersible lighting illuminates the blue gravel
  • The filtration chamber includes media and motor
  • A glass top and acrylic tank


  • The unit doesn’t include a heater, and adding one fogs the glass top
  • Very expensive

– – –

10. Tetra ColorFusion Aquarium 20 Gallon Fish Tank Kit

Tetra ColorFusion Aquarium 20 Gallon Fish Tank Kit

Our final tank on the 20-gallon list for Glofish is the Tetra ColorFusion Aquarium, which features a color-changing light so your Glofish can really shine. As a bonus, this is a complete kit with all the equipment, such as filters, heaters, and more, to get your tank set up for a lovely school of Glofish tetras. 


  • Tank dimensions: 27.88” x 16.13” x 20.38”
  • Kit includes: UL heater, Whisper 20 filter, color-changing LED
  • Hinged lid


  • The tank is well-appointed, with enough space for 8 – 9 Glofish tetras
  • The tank length is ideal for racing fish
  • The LED light fits conveniently in the low-profile lid
  • The set includes a Whisper 20 filter, UL heater, LED color-changing light, and synthetic plants


  • The filter is a bit loud

– – –

Setting Up My 20 Gallon Glofish Aquarium

how many glofish tetras in a 20 gallon tank

Once you have selected the type of Glofish you want to keep in your Glofish tank, you will have to decide on factors such as tank size, decorations, heater, lighting, filter, etc. First, look at setting up the perfect tank for your Glofish.

Tank Size, Shape, and Type

Setting up a 20-gallon aquarium for Glofish is similar to most tropical fish’s requirements. However, Glofish tetras are highly active fish. They love swimming, doing laps in the water, and may even try to leap out of the tank (though it is rare). 

When setting up a tank for them, choose a rimless aquarium instead of a rimmed one so that you will enjoy unobstructed views of their antics.

Opt for a horizontal tank instead of a taller, vertical one. It’s wise to place the tank on an aquarium stand and place a styrofoam sheet for extra support. Adding a lid is ideal to prevent the more adventurous ones from leaping from your tank.

Substrate options: Sand or Gravel?

Glofish love sand and gravel, so these are a must in the tank. While sand tends to layer the tank’s waste on top, gravel is easier to clean as it doesn’t get sucked up so quickly when you siphon your tank. 

Start by rinsing your gravel substrate, removing any residue or contaminants before adding it to your tank. Moreover, you can add other decorative elements to the stone, too, such as sculptures and plants


You must remember that decorations such as stones, caves, huge rocks, and plants take up quite a bit of the available aquarium space. To compensate for this occupied space, you require a slightly bigger tank. Adding a piece of driftwood is advisable only when you have enough room for your fish to swim around it.

Also Read: 10 Best Gravel for Aquarium Plants:


Glofish does not have any specific lighting needs. A regular LED light in a blue shade works fine. If you want the ‘glow’ of the Glofish to be more prominent, you can even add a black light. During the day, the Glofish doesn’t need a lot of light – you can use a blue LED light to highlight the fish.


No matter how small the tank or the fish is, a filter is essential in setting up a tank. Even though Glofish are not prominent mess creators, they still need a primary sponge filter. The filter will ensure that the water does not have high nitrate levels and cycle out the tank waste. It will also help circulate the water and improve the water flow, encouraging oxygenation.


Glofish tetras come from places with a hot climate. This means that the average water temperature is usually high. Therefore, if you keep Glofish tetras in a tank at home, you will have to provide a heater for them to feel more comfortable. A 50-watt heater (whether submersible or external) will keep your Glofish tetra warm.

Also Read:


Glofish are captive-bred and, in most cases, will live for 2 – 3 years if well cared for. A 20-gallon tank allows 9 – 10 short-finned Glofish to swim freely. 

We would always recommend choosing a slightly bigger tank if you keep the maximum count of Glofish, even though 20 gallons is enough. This is because tank overcrowding can lead to depressed and sickly Glofish tetras. 

Keeping too few Glofish in your tank can impose loneliness, which is bad for these shoaling fish. So establish a healthy population of Glofish with enough space to move, ensure their tank is clean and at the right temperature, and enjoy watching their daily races.

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