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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I’ve been wondering what the actual stocking densities of glofish tetras and danios are. Currently I have a 10 gallon tank with 10 danios in it and I was looking into getting some tetras. I read on the glofish website that they recommend 2 danios per gallon of tank space and 1 tetra per gallon of tank space. Other websites provide different stocking densities of each fish and even a glofish representative that I talked to gave me a different stocking density than what was posted online and recommended that I get a bigger tank. I was thinking of getting… Read more »

Lau COro

With a 10 gallon tank, stick to what you already have. If possible you may want to find a larger tank up to 30-40 gallon in order to safely add more fish. I myself have 14 Glofish, two algae eaters, and two snails in a 75 gallon along with decor. The larger the tank also means less chances of changing parameter of water. Look on craigslist, there area ton of people getting rid of large tanks at a steal. But please do not add more fish to your 10 gallon tank.


My daughter has had a pink glofish for over a year. We’ve kept Carl in a small bowl in the kitchen and he’s been healthy and happy. He has a great personality for a fish and I’ve become quite attached to him. We just moved him to a 10 gallon horizontal tank as you’ve recommended with a heater and filter and low decorations. He’s been flying around side to side exploring his new tank. We’d like to add a few more glofish. How Can I tell what species of fish he is to determine the best match for him? Also… Read more »


I bought a 20 gallon tank in July for my daughters birthday and last weekend we went to get the fish for it. We now have 6 fish (5 glo tetra and 1 black skirt). Currently we have 2 small fake plants in the tank. My daughter wants a few more fish and when I asked the gentleman at the pet store he recommended 2 small catfish to help clean the tank and maybe a betta. He suggested adding the catfish a week after the Glofish and then the betta on the third week. I have had betta before but… Read more »

Nelsen Witt

Hello! I know this article is older, but I’m trying my best to give my sister the coolest and healthiest glofish tank I can. I got a 36 gallon tank. How many of the fish can I put in?

I figured 5 tetras and 5 danios. OR 10 barbs.

Could I do more. Or mix barbs in with danios or tetras? I cant get plants, so what type of plastic decor is ok?

Sorry. Just want to have as much knowledge as possible. Lol


Hello! I found this article as I was researching more options for my daughter’s fish. I’ll admit we jumped in and went off the advice of an employee at the pet store and now I’m wondering if that advice was sound. They recommended a 5 gallon tank for 2 glofish tetras, they’re the larger tetra, and a smaller version of a pleco. One of the tetras passed yesterday (and was promptly replaced so my daughter wouldn’t be upset) and now I’m wondering if our tank setup isn’t correct. We have a 5 gallon tank, with filtration, heater, and bubbler. I… Read more »

Confused glofish

Hello! We recently set-up a 20 gallon tank and got 5 glo-fish and a plecko. One of the glo-fish is pretty aggressive towards the other glo-fish. They have some plants to hide in, but we’re wondering if we need to get one or two more to make the school bigger, or if it’s just natural to have one fish that is going to pick on the others. We can also take the aggressive fish back and get a different one. Any thoughts? We want our fish to be happy and healthy.


Hello! I currently have my golfish in a 55 gallon tank but I was thinking of getting a smaller tank because they seem aggressive towards each other! I have 4 danios, 4 tetras, and 1 shark. Do you think getting a smaller fish tank would be smart, or should I just get more fish for a bigger school?


New fish keeper here… Trying to find some advice and I seem to get mixed comments on this. I purchased a 20 Gallon Long tank and currently have 6 Glo Tetras in it. Daughter would like a school of Danios as well since they seem more active. Would 6 of each be too many for this tank? When I checked the stocking website with my tank size with the brand of filter I have it showed 60% stocked. With weekly 21% water changes.


Getting a 20 gal long aquarium for our new family of Glofish, how many of each kind will it hold and everyone staying happy and healthy? Is there a certain type of school that we should add first? Also what is the best type of substrate for glofish? Thank you so much!


Good Afternoon! I just recently found this article and now I am wondering if I may have taken bad advice from the people at the fish store! 🙁 I have a 55 gallon tall tank with a canister filter and heater. I also have several larger decorations that have plenty of hidey holes and swim throughs. I have 3 air rocks as well to keep the air flowing. I currently have 7 Glo Fish Danios, 6 Glo Fish Barbs and 2 Glo Fish Sharks. I am wondering if I may have over stocked the tank, they all seem to be… Read more »