What is the Best Tank Size For Guppies?

The size of your aquarium is just as important for your guppies as water quality and tank dynamics. Most novice guppy owners fail to realize that a too-small tank will cause guppies discomfort even if they’re not overcrowded.

Guppies need a more spacious environment and enough water volume to swim comfortably around their habitat. A large enough tank will create the impression of freedom, keeping your guppies in a healthy state of mind.

Overcrowded tanks, just like small ones, will stress your guppies and trigger a territorial behavior that may lead to aggression.

A too tank that’s too large will also come with its own issues, like making access to food more difficult. Guppies tend to search their surroundings for food, and if the tank is too large, they may have difficulties finding it.

To prevent both these problems, you should set up the ideal tank size for your respective guppy population. The more guppies you have, the larger the tank should be.

Today, we will discuss ideal tank sizes for guppies and look at the main problems arriving with improper aquarium sizes.

What is the Minimum Aquarium Size for Guppies?

The minimum you can go for a guppy aquarium should be 10 gallons. This is perfect for accommodating a guppy population of 5 to 10 specimens, depending on their size. If the guppies are larger specimens, you shouldn’t keep more than 5. If they’re smaller, more will work.

Over 10 will lead to overcrowding which comes with its own risks and problems. We will discuss these later.

A key note here – the 10-gallon recommendation can be a bit unintentionally deceiving. When we say 10 gallons, we mean that’s the total amount of water the tank will hold. In reality, however, a 10-gallon tank will never hold 10 gallons of water, not even close.

Ask Archimedes. Every object submerged in a fluid will displace a volume of fluid equal to its own volume. Fish, plants, rocks, and aquatic ornaments will all increase the water level in the tank dramatically. This will force you actually to use less water than you should.

As you can see, you can only stick to the 10-gallon rule if you minimize the number of objects you place in the tank. But you can’t keep guppies in a tank devoid of any environment. You need to have some form of subaquatic flora, a substrate, and rocks to make your guppies comfortable and provide them with hiding places.

For this reason, I would recommend tanks larger than 10 gallons even when keeping the minimally recommended guppy population.

What’s the Best Tank Size for Guppies?

I would say that the ideal aquarium size for your guppies is 40 gallons. Here are the main reasons why:

  • Allows for more decorations – The goal is to provide guppies with an as natural as possible environment. Big rocks, algae, aquatic plants – all these will enrich the guppies’ environment, allowing them to feel safe, comfortable, and at home. With a higher water volume available, you no longer need to worry about water displacement due to adding plants and decorations.
  • Lowers the risks of overcrowding – Many guppy owners struggle with overcrowding problems, affecting the tank dynamics. Guppies and other fish may become more territorial and display more aggressive behavior as a result. Not to mention, overcrowding leads to faster fish waste accumulation which may pollute the water. Having a larger tank will provide guppies with more space, minimizing the risks associated with overcrowding.
  • Mixing fish species – Having multiple fish species is always better than sticking to a guppy-only tank. Guppies are highly sociable animals, and they get along with a variety of other friendly species. A 40-gallon tank will allow you to mix different fish species, providing the aquarium with unique fauna.
  • Ensure stable water chemistry – More water volume translates to stable water chemistry. The risk of ammonia increase will be significantly lower, keeping your guppies safer and healthier in the long run.

The main problems, as I see them, include money and experience. A larger tank will obviously cost more than a smaller one. Sometimes a lot more. If you treat growing guppies as a second-hand hobby, you might not want to invest too much in the tank.

The other problem is the lack of experience in growing guppies. If you’re new in the business, you probably don’t have the confidence necessary to get a 40-gallon tank and a dozen or more of guppies. Not to mention mixing several species, each with their own environmental requirements and feeding behavior.

But, if you’re ready for the task, getting a 40-gallon tank is the best thing you can do for your guppies.

How Many Guppies Should I Keep in a Tank?

This is the main concern that all guppy owners should consider before setting up the tank. Most guppy breeders will focus on aspects like water quality, oxygenation, temperature, feeding schedule, etc., and ignore the downsides of overcrowding.

Having too many fish in the aquarium can come with a variety of issues, affecting the entire guppy population.

Overall, here are the main aspects to consider when setting up the tank:

  • The 1-inch-of-fish-per-gallon rule – This is a classic rule of setting up the tank within the ideal population parameters. Calculate 1 inch of fish per 1 gallon of water, and you will find the perfect balance between the number of guppies and the necessary water volume. Just make sure you don’t mess up the calculations. Like we’re already discussed, a 40-gallon tank won’t offer 40 gallons of water. The tank will hold numerous other things, including a filter, water heater, plants, algae, rocks, and even the fish themselves.
  • Watch out for gender distribution – A male-only tank will come with poor population dynamics since males are natively more territorial and aggressive. On the other hand, guppy males are more colorful and will provide the tank with a more vibrant look. You need to weigh in the pros and cons and see if it’s worth having a male-only tank. I would say that, with enough consideration, you can have a male-only tank. Just make sure that your guppies have a lot of room at their disposal to minimize aggression.
  • Uncontrolled breeding – A mixed population will also come with its own challenges. Females can give birth to 5 to 20 or more fry every 30 days. In some cases, those numbers can jump to 100-200 fry. If you do not control the breeding process, you will have a lot of fry swimming around, leading to overpopulation. To prevent that, always monitor the females and remove the pregnant ones when approaching labor. You can reintroduce them to the tank once they’ve given birth and only keep the fry with the better genes, coloring, and overall traits.
  • Monitor waste accumulation – Having multiple guppies translates into more fish waste accumulating on the substrate. This can increase the ammonia levels to dangerous values, poisoning the fish and killing them in the process. The more fish you own, the bigger the risks and effects of ammonia poisoning. To prevent that, I suggest monitoring the ammonia levels constantly. You should also check water oxygenation and clean the tank regularly to prevent the formation of harmful bacteria.
  • Supervise the tank dynamics – A 40-gallon tank will provide you with more space to add various fish species. Some may be larger than your guppies, which is both good and bad. It’s good due to the diversity but bad because of the risks of bullying and aggressive behavior. You need to make sure that other fish species don’t attack your guppies or affect their feeding behavior in the process.
  • Check for early signs of illness – Many fish disorders are contagious and can affect the entire population fast. They are also deadly and can kill the entire tank, including other fish species. Pay attention to early signs of fish illness, quarantine the sick, and euthanize them if the treatment doesn’t work.

As a short summary, you should make a few calculations before getting the tank and the guppies. Make sure each guppy gets a gallon of water at the very minimum.

Be careful, however – other fish species require more water and may interfere with your guppies’ requirements. You should always take into account each species’ needs to ensure a balanced environment for all fish.

Can You Keep Guppies in Glass Bowls?

You probably can, but I wouldn’t recommend it. A glass bowl would probably hold around 1 to 3 gallons of water. This will come with several problems, including:

  • A limited number of fish – Based on the 1-inch-per-gallon formula, you can keep, at most, 3 guppies in the bowl. This is the best scenario where you have 1-inch-long guppies. More realistically, you will have 1 or 2. This can, in time, affect the guppies’ wellbeing.
  • Water quality – The less water you have, the dirtier it will become. You will probably need to change it daily, which will cause your guppies a lot of stress. Since the space is too small, fish waste and unconsumed food will accumulate fast, increasing the ammonia levels fast. I seriously doubt you can maintain water quality without significant effort.
  • Poor quality of life – Guppies know when their environment is too small. They may be dumb since they’re fish, but not that dumb. Not to mention, their environment will have limited vegetation due to the lack of space, causing guppies to stumble upon each other constantly. They will have an increased feeling of overcrowding, which will lead to stress, illness, and potentially death.

I agree that the bowl is easier to handle since you can move it around the house with little effort. Such habitat is, however, unsuited for guppies or any other fish species for that matter. I recommend keeping the bowl for species more well suited for such environments like snails or shrimp.


Setting up the tank properly can make a huge difference in your guppies’ quality of life. As I have recommended, assess the size of your fish, how many you have, and their water volume requirements before purchasing the tank.

This will allow you to set up a comfortable subaquatic environment, providing your guppies with the ideal living habitat.

If you don’t know how to set up your tank, what equipment you need, or anything related to the topic, check out my other articles on the issue.

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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