How Many Glofish In A 20-Gallon Tank?

I know glofish has the potential to attract anyone’s attention, how cannot they? These glofish are so adorable, beautiful, bright, and colorful that it is not a new thing to know you fell in love with them. But falling in love won’t give answers to many questions you have in mind. The numbers, the maintenance, the school size, etc. raise questions about glofish. How many glofish in a 20-gallon tank? What school size of glofish is ideal? What happens if glofish are not kept in a group?

Each type of glofish prefers specific numbers of them in a school in a 20-gallon tank. So, the number of glofish varies according to the type of glofish you select and want to accommodate in the tank. Based on the size and type of glofish, you can keep 2 to 10 glofish in the 20-gallon tank with certain precautions.

And of course, you have researched well and have probably seen the suggestion of using 20 gallons tank or more. However, this much information is never enough, I know that because I have been through it all.

In this article, I will help you to understand how many glofish to keep in a 20-gallon tank. Furthermore, you will find the answers to why, what, and so on about the glofish accommodation.

Let’s get started, shall we?

How Many Glofish In A 20-Gallon Tank?

Okay, as I mentioned already, it depends on the types of glofish you want to keep in the tank. You might already know there are 4 distinct types of glofish namely glofish danios, glofish tetras, glofish tiger barbs, and the biggest one glofish rainbow sharks.

So, you see, their size and preference of tank environment determine the number of glofish you can keep in the 20-gallon tank.

Let’s know about them individually according to the number you can keep in the aquarium with 20 gallons capacity.

I have also written an article on How To Setup A 20-Gallon Fish Tank: Livestock and Equipment List [2020]. You might need it while setting up the tank for your glofish.

How Many Glofish Danios In A 20-Gallon Tank?

Here we are talking about the very first patent breed of glofish, the very first genetically engineered glofish: Glofish danios.

These glofish are quite active and wonderfully playful so you can imagine the space they will need in the tank.

And like danios, these glofish danios are schooling fish as well so, say hello to your friendly and social glofish.

Now coming to the 1-inch one-gallon rule which clearly says that for each inch of fish you need to keep 1 gallon of water.

Furthermore, our dear glofish danios reach the maximum size of 2.5 inches and hence we apply the one-inch one-gallon rule.

So, according to the rule, you can keep 5 to 10 glofish danios in the 20-gallon tank, however, 10 would be pushing your limits.

Stay with the good number 6 or 8 and you will have a happy glofish swimming in a tank along with its school.

Also, if you are a beginner aquarist who barely has any idea about cycling the tank, stay with the number 4 for glofish danios.

How Many Glofish Tetras In A 20-Gallon Tank?

Okay, now it is time to talk about my personal favorite type of glofish i.e., glofish tetras, and its number in a 20-gallon tank.

First thing first, like glofish danios, glofish tetras too have genetically inherited the schooling nature from their parent breed.

However, these glofish tetras are not as friendly or social as glofish danios. But keeping them alone in the tank, let alone the big tank like 20 gallons is out of the question.

So, let’s talk numbers here, shall we? Like glofish danios, these glofish tetras grow up to 2.5 inches in size which in turn means 6 to 10 of them in a 20-gallon tank.

But please remember to put plants like java moss, etc. in the tank of these shy glofish tetra to give them hiding space.

How Many Glofish Tiger Barbs In A 20-Gallon Tank?

Glofish barbs are totally another story in terms of temperament compared to glofish danios and glofish tetras.

Although these three have a few features in common. Glofish barbs are semi-aggressive yet schooling fish.

These glofish are the bully fish so they will do well with their own kind and will nip other fish present in the tank.

Now, coming to the size of these glofish, glofish barbs can reach up to 3 inches. So, their accommodation number in the 20-gallon tank is around 6 to 8 of them.

How Many Glofish Rainbow Sharks In A 20-Gallon Tank?

Glofish Rainbow sharks are not small as other glofish so we cannot go for the schooling number here.

And, you can imagine how the number will vary with the glofish that has a shark in its name.

These glofish rainbow sharks can grow up to 6 inches so as per the rule of one-inch one-gallon, you can keep 2 glofish rainbow sharks in the tank of 20 gallons capacity.

But let’s come back to reality and leave the technicality behind this time because 20- gallons tank is not even sufficient for one glofish rainbow shark, let alone two of them in the real world.

These glofish are bottom dwellers and spend most of the time on the bed or substrate of the aquarium.

It will search for food and lazes out on the bottom of the tank and 20-gallons is not sufficient to keep up with their activities.

These glofish rainbow sharks ask for at least a 55-gallon tank and more to live and thrive in captivity. They will be restless and stressed when you keep them in a smaller tank.

Provide them ideal conditions along with the optimum tank size so that you can enjoy their company at your home.

Table Showing The Number Of Glofish In The Tank According To Their Type And Size

Types Of Glofish Size Of Glofish Number Of Glofish In 20 Gallon Tank
Glofish Danios 2.5 inches 5 to 10
Glofish Tetras 2.5 inches 10
Glofish Barbs 3 inches 6 to 8
Glofish Rainbow Sharks 6 inches 2

Why Do Glofish Need To Be In Groups?

Well, human beings are social animals, but what happens when they are left alone? Please don’t say Tarzan because we aren’t getting talking animals here anytime soon.

So, why would anyone expect schooling fish like glofish danios, glofish tetras, or glofish barbs to live alone rather than in a group?

These glofish thrive when they are kept among their own kind and you will have quite a happy and active aquarium too.

Glofish tiger barbs are kind of aggressive when they are separated from their school. And they behave like a good and polite child when you give their family.

Loneliness in fish is a real thing and it can impact their mental health more than you can imagine. So, be a good glofish parent and give your fish what they need.

Trust me, you will love seeing a group of colorful glofish swimming around in the tank making their tank more vibrant and livelier.

What Happens If I Overcrowd My 20 Gallon Glofish Tank?

Well, you will live through a nightmare in real life when you overcrowd a tank with fish. How would you feel if you are forced to live in a room with a whole bunch of people for your entire life with a limited food supply?

Now, you know the feeling. Your tank will be an aquarium version of the reality show ‘Survivor’ when you keep fish more than the tank can hold or your fish can adjust in with limited resources and space.

Too much stuff in one place can suffocate anyone, let alone the fish. Even the waste production reaches its peak when there are many glofish excreting waste materials in water.

Even the beneficial bacteria present in the tank and filter media will not be able to perform aquarium nitrogen cycle and convert all the ammonia into nitrate.

Likewise, aquarium Ammonia poisoning and pollution will cause diseases in the fish and can turn fatal in a short duration.

Ammonia and nitrite present in the tank can cause the death of your glofish even if it is low concentration.

What Happens If I Keep Less Number Of Glofish In The 20 Gallon Tank?

Well, it won’t be a that big problem if you keep slightly a smaller number of glofish in the tank than it is recommended. Hey, I said ‘slightly’ remember that so go for only a marginal decrement of number.

But glofish are quite social and they thrive when you keep these glofish in a group of at least 5 or 6. When you keep them in a group smaller than 4 then the problem arises.

These glofish love to stay in a group of at least 6 and feel secure when they are around their own kind. Predators can easily attack 2 or 3 glofish but hesitate and back off when they are in a group.

Less number of glofish in such a big tank as 20 gallons, can be stressful for these tetras and if you are talking about less number around 6, then it will actually be a good thing.

Lesser glofish in the tank means more space for the 6 glofish to swim in and as active as these fish are, they will most definitely love it.

Tank Requirements Of Glofish

There are few things you need to look at when you are petting glofish in the tank at your home. They might be hardy and adjusting but caring for them can come in handy.

Let me help you with the elaborated detail about the basic needs of glofish in an aquarium.

Water Temperature For Glofish In 20 Gallons Tank

Let’s start with the basic, the temperature preference of glofish between 65 F to 75 F. And your tank to stay at the constant ideal temperature, you must install an aquarium heater.

The aquarium heater is a piece of must-have equipment when it comes to maintaining temperature for tropical freshwater fish.

You can use Aqueon Adjustable PRO Aquarium Heater or Hitop Submersible Adjustable Aquarium Heater for the glofish tank with 20-gallon capacity.

Filtration For Glofish In 20 Gallon Tank

Like any other tropical fish, glofish are sensitive to the presence of ammonia, nitrite, or any other type of pollution in the tank.

You have to cycle and mature your glofish tank beforehand so after adding the glofish you may lose them while filtering.

If you do carelessness with the filtration of the tank before and after adding glofish, you might bring death to glofish.

Many issues like cloudy and foamy aquarium water along with the disease-causing agent like bacteria, viruses welcome themselves in the glofish tank.

Aquarium ammonia poisoning and water pollution are the main villains for the death of any fish in the aquarium.

Tetra Whisper IQ Power Filter will unload the burden from your shoulder and I highly recommend you to use this filter for your 20-gallon tank.

25% of Water change is quite necessary to do once every couple of weeks but remember not to overdo it.

Decorations And Substrate For Glofish In 20 Gallon Tank

Glofish prefer black gravel with fluorescent accents in their tank along with the number of plants.

Spectrastone Special Black Aquarium Gravel, you can buy this substrate from and keep it in your glofish tank.

Java MossJava FernAmazon Sword, etc., can be your go-to plants when it comes to decorating a glofish tank.

You can also give driftwood, and other few décors in the glofish tank but do not overcrowd the tank with all the decorations.

Lighting For Glofish In 20 Gallon Tank

When it comes to fluorescent fish like glofish, you can go for both blue LED as well as the black light. But remember the lighting should be dimmer and should have a darker vibe.

And most importantly, you only need to turn the lights on for 10 to 14 hours, any more than that your glofish will start to lose color and activeness.

The best light for these glofish is the LED light that is a combination of both white and blue lighting.

GloFish Cycle Light For Aquariums Up To 20 Gallons, With White, Blue, And Black LED Lights is the ideal light that you can easily find and buy from

Tankmates For Glofish

Choosing the tank mates for these glofish is quite easy. Just look at the size and the type of glofish you have, and choose another fish of similar size and prefer similar water parameters.

Other danios, barbs, tetras along with fish like angelfish or say any other freshwater fish will do a great job at becoming the tank mate of these glofish.

But remember not to overcrowd the tank as overcrowding can result in serious issues in your fish health as well as the tank.

Diet For Glofish

Glofish need a good, healthy, and balanced diet to retain their color. Look for food that is high on carotenoids and beta carotene when it comes to choosing food for glofish.

However, there is another thing you need to do for them while feeding glofish. You need to feed them a variety of food as they cannot and do not prefer to eat the same type of food every day.

Flakes, pellets, frozen, and live food is the various option you can choose from commercially.

If you are free and ready to get your hands dirty, you can prepare fish food for them at home as well.

Just research well about the type of glofish you have along with their dietary need. Also, search recipes to make homemade food properly.

Frequently Asked Questions

I know you have more questions lingering back in your head and I am here to help. So, I am trying to answer few questions that people ask the most about glofish. Hope this will help you.

Can Glofish Live With Other Fish?

Yes, apparently the schooling and social nature of these genetically engineered glofish are the same as the fish they are engineered from.

Glofish can live happily and with no issues with fish that are similar in size and has the same temperament.

You can keep these glofish in the community tank along with other tetras, danios, Rasboras, small barbs, and of course with each other.

How Many Glofish Can Be Kept In A 5-Gallon Tank?

Technically speaking, you can house 2 glofish danios or glofish tetras, or glofish tiger barbs in the tank with 5 gallons water capacity.

But I wouldn’t suggest you try this or experiment with it. Glofish are schooling fish and will do well in the school of 6 members.

Any less than that can upset them and turn them into a lethargic, sluggish, starving fish with very few activities.

What happens if you are kept in a new environment with no familiar faces or with very little human contact? Alike human beings, these glofish get scared when they are less in number.

So, think wisely and drop the idea of keeping a 5-gallon tank in your home. If you really want to keep glofish, go for the tank with 20 gallons capacity or more.

Can Glofish Live In A 10-Gallon Tank?

Yes, as a matter of fact, these glofish can live in a 10-gallon tank except for the glofish rainbow shark. (they can barely stay in the 20-gallon tank). However, the smaller number of fish will make the glofish sad and the school size won’t be ideal either.

The tank with 20 gallons capacity is minimum ideal for the school of each glofish type, be it glofish tetra, glofish danios, or glofish tiger barbs.

But don’t get your hopes up with a glofish rainbow shark. They have a shark in their name, what else can you expect?

Can A Glofish Live Alone?

Yes and no. Yes, because these glofish can live in the tank alone for a while but not for long. As you know now, glofish are schooling fish and are actually quite social so they will hate when they are left alone.

Glofish will be lethargic and stop eating when they are kept alone in the tank. So, you can imagine how long will a hungry, starving, sluggish, and inactive fish will live in captivity.

These glofish will die of loneliness and it is a real thing. Sometimes, I feel like fish have the same feeling as human beings. Don’t you?


In conclusion, glofish are special fish that are quite playful and active, so they will prefer a good company with familiar faces around them. It can be glofish tetras, barbs, danios, or rainbow sharks, either way, they will want to be in the company of their species. Any social being when left alone, there will be consequences you won’t like. So, be careful with how you treat your glofish or how you keep it in the tank? Follow the lead, read the articles I suggested, you’ll do just fine, trust me on this.

And, if you have queries or questions related to glofish, any types of glofish other than I have answered above, hit me up on the comment section.

I will try to solve your problem or we can find a solution or answer together.

Good Luck!

Happy Fishkeeping!!!

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