How Many Glofish Are Actually Recommended Per Gallon?

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First of all, let me point out that the “inch per gallon” rule does not apply to Glofish. Moreover, that rule is not and will never be correct for any species of fish. Imagine putting a 10-inch fish in a 20-inch (10 gallons) tank. With good filtration, It will probably survive, true, but will it be happy?

Will Glofish be happy in a one gallon tank? Short answer, probably not. One of my personal rules on the matter is that this is not a hobby, these are our pets. We need to treat them with love and care. They deserve to be happy. But I digress. Let’s dive right in.

Exactly how many Glofish will be alright in a gallon of water?

There are a couple of things you need to know about Glofish before we proceed:

  1. Glofish are schooling fish – they need the comfort of living in a group and swimming in a group.
  2. Glofish are not one species of fish – Glofish is an umbrella term for more than one species of genetically modified fish that end up glowy. Most popular ones are the Black Skirt Tetra and the Zebra Danio.

Before we discuss a suitable tank size for any Glofish I first must point out the size and characteristics of each separate species that is included under the umbrella term “Glofish”:

  • Glofish Danios, which are essentially Zebra Danios, grow up to 2.2 inches of body length (5.6 cm).

    This species needs to stay in groups because they form complicated social hierarchies among them. They are also fast swimmers and need lots of horizontal space for swimming.

    glofish zebra danio near the water surface

    by TitanicsAnInsideJob

  • Glofish Tetras, which is a variation of Black Skirt Tetras, reach just about 3 inches as adults (7.62 cm).

    This species also needs to stay in groups of 6 or more in order to lead a happy life.

    close up of a pink glofish black skirt tetra

    by TheeBlackSheep

  • Glofish Tiger Barbs, are just that – Tiger Barbs.

    Tiger barbs grow to be around 3 inches in body length (7.62 cm). Tiger barbs are known menaces in the fishkeeping hobby because they tend to become very aggressive if not kept in groups.

    When they have their own group the aggression is spread out among the members of the group and there is a lesser risk of injury for the fish.

    two glofish tiger barbs swimming near the aquarium's glass

    by TheeBlackSheep

  • Glofish Corydoras are actually Bronze Corydoras which is a type of small catfish that grow up to be 2.5 inches or 6.35 cm.

    Bronze cory catfish are social fish and need to be kept in groups of at least 5 specimens.

    a bright green glofish corydoras

    by Liddojunior

  • Glofish Pristella Tetras are ordinary Pristella tetras made to glow.

    These fish reach up to 1.9 inches in length when fully grown (~4.8 cm). Pristella tetras need to be kept in groups of their own to live comfortably.

    close up of a golden pristella tetra

    by rmarkham (I could not find a good photo of a glofish Pristella tetra so an ordinary will have to do)

  • Glofish Betta fish are your regular Betta Splendens made glowy.

    The size of an adult Betta fish is roughly 3 inches (7.62 cm), but some specimens never grow past 2.5 inches (6.35 cm). Bettas are mostly solitary and many of them have anger issues…

    These fish are best kept singly if you’re a beginner to fish keeping.

    glofish betta near the surface of its fish tank

    by Amaalecule

  • Glofish Sharks are what is known as Rainbow shark in the hobby.

    They are not real sharks but do closely resemble one. Rainbow sharks grow to be the largest of all other types of Glofish, closing in on 6 inches of full body length (15.24 cm).

    Rainbow sharks are aggressive and don’t like other fish entering their territory, which is typically the bottom of the tank.

    glofish rainbow shark looking for food on the bottom of its aquarium

    by FloatingNine

With this out of the way, I can now discuss appropriate tank sizes for the different types of Glofish.

Through trial and error, the aquarist community has reached an agreement on what would be a comfortable home for each of these fish.

Most experts agree on the following:

  • Glofish Danios should be put in nothing short of a 20-gallon “Long” tank. Keep your Danios in groups of 7 to 8 so that they can form their hierarchy.
  • Glofish Black Skirt Tetras should be kept in a 15-gallon tank as the bare minimum. Get 6 or 7 specimens and let these social fish form a group.
  • Glofish Tiger Barbs need at least 20 gallons to thrive but it’s recommended you get them a 30-gallon tank for a comfortable life. Keep these fish in groups of 6 to 7 specimens or they will suffer a shortened lifespan, same as every other social fish.
  • Glofish Corydoras need a minimum tank size of 10 gallons. However, most experts agree that they truly thrive in the 20-gallon “Long” tank. Keep them in groups of 5 but 6 or 7 is better.
  • Glofish Pristella Tetras need to be put in a 10-gallon tank as the minimum. To make their group of at least 6 truly comfortable, however, you’d want to keep them in a 15-gallon aquarium.
  • Glofish Betta fish are ideally kept in a 5-gallon tank as the minimum. If you go with the 5-gallon tank, keep Bettas alone, at least at first. When you get the hang of looking after them you can maybe add some tank mates to their tank.
  • A single adult Glofish Rainbow Shark needs a 55-gallon tank to thrive. These fish will occupate the bottom of their tank and won’t be happy with other bottom-dwellers. Keep your 55-gallon tank’s bottom reserved for a single specimen.

Taking the specific needs of each species of Glofish we can come to the conclusion of how many gallons each individual fish needs. Here they are:

  • Glofish Danios need 3.3 gallons per individual. Preferably living in a tank with enough horizontal length.
  • Glofish Black Skirt Tetras need 2.5 gallons per individual.
  • Glofish Tiger Barbs need 3.3 gallons per individual at the minimum. Ideally, you’d give them 5 gallons per specimen.
  • Glofish Corydoras need 2 gallons per individual.
  • Glofish Pristella Tetras need at least 1.7 gallons per individual.
  • Glofish Betta fish need 5 gallons per individual. Keep in mind that if you put 2 male Bettas in a 10-gallon tank it will likely end in disaster. However, putting 2 males in a 20-gallon tank has a decent chance of working if the tank is decently planted.
  • Glofish Rainbow Sharks need the whole bottom footprint of a 55-gallon tank per individual.

Get the long tank and mind decoration


by lindsayarmstrong

Most Glofish species are highly active and like to swim around a lot. And since they can’t be kept singly, you can’t put a single specimen in a 3-gallon aquarium.

In most cases, this leaves a 10-gallon tank (and everything below that) out of question, with the exception of Glofish Bettas and Corydoras.

Keep in mind that decorations take up space and reduce the overall water, available to fish. Sticking a considerably large piece of driftwood in your tank can be beautiful but it will reduce the swimming space even further.

Click the link if you want to learn where to find the perfect piece for your aquarium, by the way.

You’d also want to take into consideration that the glowing Danios like to speed around in your aquarium and need more horizontal space.

If they are your Glofish of choice you’d want to have a long fish tank.

Both Balck Skirt and Pristella Tetras are quite active (and attractive) swimmers as well.

If you plan to get the bare minimum and don’t own other fish a 10-gallon tank won’t be enough.

From my personal experience, it is always best to scale up things by a level.

I always liked to keep my fish tanks stocked at populations of 70 to 80% of the maximum the tank can hold.

This way my fish would reach their full potential and not feel confined in any way.

If you do, by any chance, plan to add tank mates to your Glofish aquarium setup you will have to get a bigger tank eventually.

More fish ideas: Top Fish to Stock a Small Tank

Why do Glofish need to be in groups?


Most Tetras and all Danios should live among their brothers.

The Zebra Dario and the Skirt Black Tetra are both schooling fish species. This means that they will coordinate their swimming and do it in the same direction.

They do this as a survival mechanism and have therefore adapted to a social environment. Living among others of their kind is key to keeping any type of shcooling fish.

Glo tetras and Glo tiger barbs are known to become aggressive when not in schools.

If you keep too few of the same schooling fish species in your new tank they will feel lonely and may even die earlier.

These are social species.

I’d encourage anyone who’s excited about having an aquarium to have at least a couple of those.

They make the aquarium feel alive and, dare I say, are more entertaining to observe than most TV dramas.

A couple of friendly reminders about keeping Glofish for our fellow beginners

Here are a few tips for proper Glofish care to consider before starting a Glo-tank:

If you’re still researching what equipment a new fish tank needs, then visit this article.

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Photo of author


Momchil Boyanov is the Founder and now Senior Editor of AquAnswers. He has over 13+ years of experience in keeping home aquariums as well as providing professional aquarium services. Momchil has had his fair share of adventures in aquarium care. He has made MANY mistakes throughout his fishkeeping journey and thus learned A LOT. Through Aquanswers, Momchil shares knowledge about freshwater and saltwater aquariums with the people within this community.

34 thoughts on “How Many Glofish Are Actually Recommended Per Gallon?”

  1. I was recently gifted a 10 gallon tank. I’ve only ever had Betta fish and I love them very much but was hoping to branch out and get something that I can have multiple of. Any suggestions?

  2. Hi there, my friend and I have a 35gl. / 6-12 in. sides
    Hexagon Shaped Acrylic Tank
    We have 12 Glo Fish-
    *Love the *Long* Fins BEST
    3 Cory Cats – 2 Albino Algea eat.
    And 2 Frogs.
    My Question- Should we Upgrade to a Rectangular if Yes?
    What Size Reccomend??
    My friend LOVES this Tank
    I find very challenging to maintain

  3. Hello, I have an 8 gallon long tank with 3 danios, have some plants, rocks, driftwood, etc. They were in a smaller tank before (basically fish got dumped on us by a relative and I took them so they did just get flushed away). My hope was the 8 gallon tank I moved them into would chill out the aggressive one – but the alpha male just seems relentless. I believe there are 2 males and one female. One of them is a bully. It chases and harasses the other two where I think they are quite stressed. Especially the other male. I believe 3 is the max fish I can have in 8 gallon long tank, from the article the tank is already too small – but I cannot get anything bigger than what I have (me even taking the fish is a source of contention). Should I try to adopt out the bully? Or maybe add a couple more danios? I stay on top of regular water changes, gravel vac and have a hob filter. I know they like to chase each other – but it seems a bit much…

    • Hello,

      I think that, if you really don’t have the option to get a bigger tank, you should consider returning the fish to a fish store altogether and, perhaps, stock the tank with something that makes sense for both you and the fish.


  4. Will 2 glofishes each of different colors but of the same species (either danio or tetra) still count as school? Or do they have to be 5-6 of the same color to be considered as a school?

    • Hi,

      Color shouldn’t be considered. At least I could not find any evidence that it played a role.

      Good luck!

  5. Hi there! Just new a real fish tank. We have a twenty gallon long. With a heater, bubble and filter. We have 5 neons, two bottom feeders, 3 pearl danios, and 2 blood tetras (they’re bigger).
    I have a male betta in a fish bowl in my bedroom. Can I add him to this tank?
    And can I get any more fish to make a school for the danios?

    • Hi Heloise,

      I would not recommend adding the little guy to that tank. In my experience, this is a recipe for disaster, even if all fish involved are somewhat well-behaved.

      Onto your second question – sure, add another 3 danios.

      Also, did you mean bloodfin tetras by any chance? Bloodfin tetras are also schooling fish, but If you add more I’m sure you’ll be pushing it.

      One final thing – celestial pearl danios do better in slightly colder temperatures than the other fish in your tank.

      I hope this was helpful.


  6. Thank you so much for this great article! We have 3 Glo Tetras in a 30 gal tank. We are moving next month out of state and our belongings will be in storage for 4 months while we wait for our new house to be built. I was thinking of getting a 10 gal tank to set up in our temporary lodging until the movers bring the aquarium with the rest of our furniture. We cannot fit it in our car. When we transport the fish we were going to use a 5 gal bucket with water from the old tank. It’s a 10 hour drive. Then we will set up the small 10 gal tank using that water when we get to our temporary lodging, slowly adding additional water. Any concerns with this plan? When we do get our 30 gal tank set up finally (in October time-frame) we want to add a few more fish to have a larger school!

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