How Many Glofish Are Actually Recommended Per Gallon?

First of all, let me point out that the “inch per gallon” rule does not apply for 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? 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 – there are many genetically modified fish that end up glowy. Most popular ones are the Black Skirt Tetra and the Zebra Danio.

That being said, here’s how many Glofish is accepted for one to keep per gallon of water:

Glofish thrive in a group so it is recommended to have at least 5 from the same species. If you plan on getting 5 to 6 Glofish then a 20-gallon tank will be suitable. Keeping them in 3, 5 or 10 gallons of water will result in poor life quality and aggression. For a 9 to 10 Glofish tank, it’s advisable to provide 30 gallons of water for living space.

Get the long tank and mind decoration

These species are highly active and like to swim around a lot. You’d need 3 gallons of water per Glowfish at the minimum.

This leaves a 10-gallon tank (and everything below that) out of question.

Keep in mind that decorations take up space and reduce the overall water, available for 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.

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 tanks stocked at 70 to 80% population.

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.

Recommended read: 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.

Which is, in my opinion, the perfect view from a fishkeeper’s perspective.

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

If you keep too few of the same species 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:

  • They are tropical – A heater is a must and so is a thermometer. Keep a water temperature of around 78°F (25.5°C). The link leads to one I like myself, but you can skim this page and find what suits you best.
  • Proper cycling – You’d need to cycle your tank for a month before adding ANY fish to it. There are faster ways to do that if you are impatient though (click the link to read my guide on using bottled bacteria). Tetra SafeStart Plus is my go-to brand of bacteria starter for cycling new aquariums. My advice here is to add 2 to 3 fish every 12 to 15 days AFTER the tank has been cycled. This way you will not overload your beneficial bacteria with ammonia. Use very little fish food during the cycling process to feed the bacteria.
  • Get the long tank – Active swimmers need the distance. Another benefit is that it will be really fun to watch them dash through your tank.

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

  1. Hi there, my friend and I have a 35gl. 24in.ht. / 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

  2. 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.

      Best,
      Momchil

  3. 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!

  4. 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?
    Heloise

    • 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.

      Best,
      Momchil

  5. 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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