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:
- Glofish are schooling fish – they need the comfort of living in a group and swimming in a group.
- 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.
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.
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.
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.
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.
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.
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.
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:
- 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 new 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 and grow it.
- 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.
If you’re still researching what equipment a new fish tank needs, then visit this article.
Rubber Lipped Pleco: Care and Species Guide for Beginners
17 Floating Aquarium Plants for Beginner Freshwater Aquarists
10 Most Expensive Betta Fish Breeds Ever Sold
How Many Goldfish Should Be Kept Together?
20 Hair Algae Eaters for a SPOTLESS Aquarium
5 Best UV sterilizers to CLEAR an aquarium (2024)
13 Easiest Fish to Take Care of in a Low Maintenance Aquarium
How to get rid of green aquarium water (algae bloom)?
Are Freshwater Angelfish Easy To Keep?
Why are there Foam Bubbles in my Fish Tank? (7 Causes)
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 swimming around and schooling without any signs of distress and no aggression, unless of course one of them gets too close to the caves that each of the sharks have claimed. Do I need to move some around to a different tank or is 55 gallons enough for what I have?
Hi Katie,
What in the article makes you think you have it wrong? I even think that you can safely add 2 more glo barbs and 2 more glo danios without issues!
Good luck!
Momchil
I was worried because I got the tall tank and 2 sharks, but I appreciate your response and feel a lot more confident about my tank community! 🙂 Thank you very much!
I thank you for reading Aquanswers!
Happy fishkeeping, Katie!
Thank you for the quick knowledgeable answers! Got one more question, but not sure if it falls under this article… I have 2 barbs that seem to be fighting/kissing… in circles. Is that an indication of an issue? They were in the same tank in the pet store and have been in this tanks for almost a week.
Hi again, Katie.
They are establishing their pecking order and checking who should be the dominant fish. This is common behavior when the school is new to the tank. It’s normal for Tiger Barbs, this is one of the reasons you want a school. This way they are occupied with their own hierarchy and any aggression stays inside the school.
I hope this helps.
Best,
Momchil
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!
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.
Hi,
It’s great that you got the 20 Long! You could get even 7 from each, without pushing it. Just monitor the Ammonia upon introduction of the new fish and, perhaps, add a little of bottled beneficial bacteria to make sure nothing goes wrong with your Nitrogen cycle.
You could also have some bottom dweller, like a small pleco species.
Regards
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?
Hi Brianna,
You should absolutely get more fish. The aggressions sparks from the fact that there are fewer members in the social structure and no the tank’s size. Bump up the numbers to at least 6 or 7 from each species, EXCEPT the shark. The Gloshark should be alone.
Regards,
Momchil
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.
Hey there,
That’s their natural hierarchy and the aggressive one is the dominant one. The more Glofish in the school – the less aggression each individual will receive. I would get 2 more if I were you.
Hope this helps 🙂
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 worry we have way too many decorations as well after reading. I would also like to incorporate a glofish shark ( I think they’re bottom feeders) at some point. What would be your recommendation for what we currently have to keep them happy and healthy? Thanks so much for your help!
Hi Stephanie,
Thanks for reaching out! I’m really happy that you guys got your fish a filter, a heater, and an aerator.
Unfortunately for your current setup, GloFish Tetras need to be at least in groups (called “schools”) of at least 5 to feel comfortable as they have their own social hierarchies. If there is no school, they become extremely aggressive and stressed because the dominant one will always harass the little company he has. This eventually leads to so much damage and stress that the rest of the Tetra fish perish. With a proper school of 5+ specimens (but preferably 7+) the dominant fish is occupied and the rest of the fish do not get as stressed.
For these reasons, my advice would be to upgrade to a larger tank, something like 20 or 30 gallons. I have an article on tank dimensions if you’d like to see how that will fit in your room. If you’d like to have a GloShark then I’d highly recommend avoiding any other bottom-dwelling fish as territorial disputes and aggression may arise. A single GloShark needs at least 48 inches of vertical length to swim in (again, check my aquarium dimensions article for reference). This is usually a 55-gallon tank or larger.
I understand this might feel overwhelming to hear. If you’re bounded by space or other resources you could just read my recommendations for safely stocking a 5-gallon tank: https://aquanswers.com/best-fish-for-small-tank-5-gallon-freshwater/
Choose something that’s beginner-friendly and interchange the fish. You could explain the situation to your daughter and she may understand?
Another thing I’d like to mention is that you should cycle the aquarium or your new fish will keep dying. “Cycling” means to give the bacteria in the water time to establish the Nitrogen cycle. Simply put, with a stable Nitrogen cycle in the aquarium, the fish won’t get intoxicated by their own poop. Did you cycle your fish tank? If not – write back to me and I will give further pointers.
Good luck!
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
Hey Nelsen,
I always encourage people to do proper research before diving into the hobby, so please don’t apologize for wanting to do everything right from the first time!
For GloFish Danios I’d say you need at least 30 inches of vertical swimming length. I checked my cheat sheet on aquarium dimensions and did not find a 36-gallon tank there, but I’m assuming it has 30+ inches of vertical length.
Therefore, you can safely mix danios and tetras. If I were after a mixed-species aquarium, I would do 7 to 8 danios and 7 to 8 Glo tetras, and possible a bottom feeder (some miniature cory or a small pleco). I would make sure the tank has decent filtration so that there are no ammonia issues.
You could also do up to 15 tiger barbs + a bottom dweller again.
As for the decor – whatever you deem interesting enough. It could be plastic plants, caves, castles…
Did you cycle the tank? Just make sure not to add all of the new fish at once. Add one school first, monitor the ammonia and nitrite, if everything is ok, add the next batch of fish. Adding some bottled bacteria when adding new fish is a sound practice as it reduces the risk of overwhelming the beneficial bacteria that convert the harmful ammonia to the relatively harmless nitrate.
Good luck!
Thanks greatly appreciated I have 5 glo danios 2 molly 6 glo tetras and 2 blue dwarf gourami’s only lost one gourami due to to much ammonia buildup an there very healthy an active im about to head out to go grab maybe three more today just did a 25% water change yesterday and added water conditioner proper p.h 7.0 an bacteria starter had a little acidic problem with water doing water check today before getting more fish
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 only as a solitary fish and 9 fish seem like a lot for a 20 gallon tank. What would your suggestion be? I do want to add at least 1 bottom feeder and I will admit I’d love to make my kid happy by adding the betta but not at the rush of making the other fish unhappy.
Hi Melissa,
Thanks for leaving me a comment and providing enough info with your initial question.
This helps me help you.
Anyway, 9 fish are not that much for a 20-gallon tank. It really depends on the fish. Glo Danios like to swim a lot and they need more vertical space. Glo Tetras also school but are not nearly as active. In your case, it would be adequate to add a betta and a bottom feeder. The bottom-feeder fish will mind its own business, and the Betta will have enough space to explore.
However, for this to work the best possible way, I’d recommend a few things.
1. You can add 1 or 2 more Glo Tetras or Black skirt Tetras besides the Betta and the bottom-feeder so that the school becomes larger. This greatly reduces the chances of aggression and fin nipping.
2. Also, for the Betta to feel comfortable I would add a little more decor and hideouts. Live plants will help you reduce organic waste in the water (which is great) and also provide shelter and interesting areas for exploration. A Betta feels very happy in a planted tank. If you don’t want to plant plants etc, you can just get floating ones.
The Water Wisteria and Hornwort, for example, require almost no care and provide beautiful hideouts for the fish. Look them up, or check out my article on floating plants by using the search bar.
So this is what I would do. The employee at the store gave you sound advice not to add all the fish at once. If you did, the bioload would overwhelm the ammonia-converting bacteria in the aquarium and the water could quickly become toxic to the fish.
Let me know if you have more questions and thanks for being a reader!
Momchil
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 What are early warning signs of territory issues. I’ll be very upset if another fish hurts Carl. Thanks!
Hi Ann,
Thank you for sharing your experience and thank you for your trust. 10 gallons is not ideal, but you could pull this off, I think.
You can do an image search of the 3 varieties of Glofish online. To summarize these are:
1. Black skirt Tetras
2. Zebra Danios
3. Tiger Barbs
…or you could possibly have a rainbow shark. The “flying around” thing makes me think it may be a zebra danio but I would not bet my shoe on that.
Anyway, find out what he is based on the photos and add the same species of Glofish so that they can form a school.
After that, you’ll need to monitor the tank for fin-nipping. An early sign of aggression is chasing, but this could also cool off with time and never really translate into actual fin damage. Close monitoring is key here.
I’d recommend getting 4 more buddies for Carl. A school of 5 could work. A school of 4 could work if you get extremely lucky with the fishes’ personalities. So I’d say go for a school of 5.
Oh and don’t forget to also monitor the ammonia/nitrite levels in the aquarium upon adding the new fish. You’ll be increasing the bioload 5 times which can cause an ammonia spike (in response to overwhelmed nitrifying bacteria). You could get a bottle of bottled bacteria to make sure this does not happen. Look up “Tetra SafeStart” for that, try your fish store or click here to see the thing on Amazon.
Good luck, and keep me posted if you feel like it.
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 4-5 tetras but I wanted to make sure that adding those tetras would not overcrowd the tank.
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.
That’s a great input Lau.
Thanks for sharing your tank details and speaking it as it is.
The large tank thing you mentioned is definitely true, I always advise my clients to go for the larger aquarium tank if possible.
pH swings are definitely not something your fish would want to experience.
Good luck to you.