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How Many Guppies in a 3.5 Gallon Tank? (Answered)

Guppies are super fun fish to keep, and they are like celebrities in the fish-keeping world. Why not! They are so easy to keep that beginners can start with them. So, if you have a small tank like a 3.5 gallon, can you keep some guppies there? What problems will you face if you do so? 

This article will explain everything about keeping guppies in a 3.5 gallon tank.

How many guppies in a 3.5 gallon tank?

Only two guppies are suitable for a 3.5 gallon tank, and in some cases, you can keep three but no more than that. A 3.5 gallon tank is not a good option for guppies as it does not have enough space where guppies can swim, feed and live freely. Water also becomes toxic fast in such small tanks.

A 3.5 gallon tank is not a good tank size for the guppies. A guppy tank should be at least 10 gallons if you want to ensure your guppies are not having any issues.

I have kept guppies since my childhood. I can’t forget the day when my first guppy gave birth to 25 tiny babies. And from then, I almost always had guppies in my house. So, I hope you will be reading a practical and insightful article about guppies.

The issues with keeping guppies in a small tank are many. Guppies are so hardy and easy to manage, so a pair of guppies can live in a 3.5 gallon tank. But the guppies will not have their best life in a small tank like that. 

I recommend that even if you keep a pair of guppies in a 3.5 gallon tank, don’t make it their permanent home. Get a bigger tank for them when possible. Guppies are not the type of fish you will just watch the feeding. 

They make love and give birth to babies very frequently. So what will you do with the new babies when you have a small tank like that? You can’t keep the babies in the same tank with other fish anyway. 

(they are lovely but show no love to their babies) Get a different tank for the babies, or you can give away the fries to your friends.

Now let’s talk about other problems you need to fix when keeping guppies in a small tank. Guppies are social fish, and they need the company to be happy. They like to live in a large group. But in a small tank like 3.5 gallons, there is not enough space to keep many guppies.

Moreover, male guppies always poke female guppies for mating (almost all the time). So when you keep two guppies in a tank, the male guppy will disturb the female one, making the female stressed.

So, if you notice your female guppies are getting stressed, you may bring another female to split the love. So, you will have three guppies in 3-gallon water. That means you will have to be extra caring to your fish to maintain their good health.

Regular water change also changes the temperature of the water. Frequent temperature change is not ideal for fish. But to keep your fish alive, you will have to do that anyway.

Guppies are fast swimmers, and they love to run and play around a tank, but in a small tank, they can not do that easily. If you want to set the heater and filter, the space becomes even smaller. 

Add some biological filter, but no need for any heater if the temperature is above 20 degrees celsius. Check out how many male and female guppies you can keep.

Male guppies:

You should not keep more than one male guppy in a small tank like 3.5 gallons.

Female guppies:

One female guppy is enough for a 3.5 gallon tank, but bring another female if the male is extra active.

Can you put guppies in a 3.5 gallon tank?

You can put two guppies in a 3.5 gallon tank, but that’s not totally ideal considering the fish comfort and maintenance. You may think that a smaller tank will be easy to maintain, but that’s not true. 

A bigger tank is a lot easier to maintain, and you will have to work on maintenance a lot less frequently than a small tank. 

In a small tank, the water gets contaminated by fish waste very quickly. So you will have to change the water more frequently. The fish will not get enough space to swim and live comfortably, but they will live their entire lives if you do other things right. 

Is a 3.5 gallon tank good for guppies?

A 3.5 gallon tank is not good enough for the guppies but still manageable with proper care. Here is a detailed explanation of why a 3.5 gallon tank is not good enough for the guppies.

Waste management:

Fish waste is the most common reason for fish passing away. That’s why it is so essential to managing the waste seriously. In a small tank, the waste contaminates the water so fast that you must change the water frequently. 

If you delay changing the water every time, you will lose your fish soon.

In a 3.5-gallon tank, there will be no effective nitrogen cycle that will help reduce the toxic chemicals from the water. That makes it more important to change the water on time.

No active nitrogen cycle:

Understanding the nitrogen cycle is an excellent plus for fish keepers. But in a small tank, the nitrogen cycle will not be effective. Let me give you some ideas about the nitrogen cycle.

Fish waste increases toxic chemicals in the tank water. To be more specific, the elements are ammonia and nitrites. If the tank water has a high amount of those chemicals, that can be fatal for your fish.

But aquatic bacteria break down those toxic chemicals into less harmful components. Some bacteria break down ammonia into nitrites. And another group of bacteria further breaks the nitrites into nitrates. 

Nitrate is less harmful to the fish, and it can work as plant fertilizer if you have plants. The amount of nitrate reduces while water changes.

So, the nitrogen cycle is mostly about caring for the beneficial bacteria in your tank. This includes not changing the whole water of the tank and cleaning the filter only with water.

But in a small tank like 3.5 gallons, you can not enjoy this fantastic biological advantage.

Fish comfort:

In a small tank, guppies will not live with complete ease. They will have less space to swim, play and feed.

How to set up a 3.5 gallon guppy tank?

Setting up a 3.5-gallon guppy tank is tricky, and it’s essential to do everything right to ensure fish are getting the maximum space from your tank. Here are some tips for setting up a 3.5 gallon tank for guppies.

Do not add any substrate like sand, gravel and stones: 

Do not add any substrate like sand, gravel and stones. Small gravel should never be used as ammonia gets trapped in the gravel, which is hard to remove. Substrates will take up space, and your fish will have less room for them.

Add a small filter: 

Add a small filter in the tank, and that’s all. Aeration can be set in the tank, but that’s not vital. Do not add any type of decoration that takes up space. 

Keep the water level high and use a cover: 

Keep the water level high and use a cover so fish can not jump outside.

Change 30-40% water every three days: 

Change 30-40% water every three days. Make sure to add dechlorinated water. Some chemicals you can find in a fish shop work great to remove chlorine from the water.

Never overfeed: 

Never overfeed. Overfeeding will damage water conditions. Make sure no food is wasted.

What fish to put with guppies in a 3.5 gallon tank?

Sadly, you should not put any fish with guppies in a 3.5 gallon tank. But if you can manage a bigger tank, you will have a lot of options. Here are the top fish you can keep with guppies.


You can keep swordtail fish with a guppy. They are similar to guppy fish, and they have similar requirements as guppies. 


Platies are also life bearers like guppies and can be kept with guppies.

Cory catfish:

Cory catfish are bottom feeders, and you can keep them with guppies.


Tetras are easy to keep, and you can keep them with guppies.

Otocinclus catfish:

Otocinclus catfish can live with guppies, but they are more sensitive to bad water conditions.

Final thoughts

3.5 gallon tanks are pretty small to keep guppies, but you can keep a pair of guppies with proper care and maintenance. Smaller tanks are more suitable for guppy fry, so it’s better to make that tank a nursery tank and get a bigger tank for the parents.