How Many Platies Should Be Kept Together? (The Quick Answer)

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When I first considered growing platies, the first question I had was how many of them could be kept in my fish tank. I knew from experience that this was a question with no definitive answer.

However, as time passed, I learned some important rules that provide a rough estimation.

So, without further ado, let’s dive right into it.

An example for a fish tank that holds too many platy and molly fish.

How Many Platies Should Be Kept Together?

When I tested different group sizes and variations of platy fish, I saw that the number of males was the best predictor of their behavior.

Over the course of a week, I tried putting in what most people recommend online, which is two females for every male (1:2 ratio).

However, after a few hours, the male started chasing and harassing the females. He kept behaving this way even after moving the group to another tank. 

Things immediately improved after I added one more female. As a side note, I saw a similar pattern in both guppy and molly fish. 

Therefore, from my experience, the ideal group size for platies is four; three females and one male. 

Depending on your tank, you can grow a larger group. However, you should maintain the 1:3 male-to-female ratio.

As a rule of thumb, it is always safer to add more females to the group than males, as males are more dominant and aggressive.

For example, you can easily increase this ratio to 1:4 and keep a group of five platies; four females and one male.

Either way, never grow an equal number of male and female platies, and certainly not a greater number of males than females.

It’s fair to say that a 1:2 ratio can work, although you’ll need a lot of hiding spots. You should also hope that the male you choose has a docile personality.

What Is The Ideal Tank Size For Platies?

The ideal tank size for platies can be calculated using the 1-inch per gallon rule.[1] The average length of a platy fish is 2 inches,[2] so each platy will require two gallons.

Therefore, a group of four platies will require at least 8 gallons of water. However, as females are a bit larger and are the majority of the group, so you need more than that.

You should also take into account the fact that your tank is probably occupied by other fish and decorations, which also take up space.

From a survey that I have conducted in online forums, more than 71 percent grow platies in a 20-gallon tank, which is also my recommendation.

So, it is best to grow four platies (3 females and 1 male) in a 20-gallon tank. If your tank is smaller, pick up to three females, with no males.

The Number Of Platies In Different Tank Sizes

To save you a lot of time and calculations, here is a simple table that gathers the most common tank sizes, and the number of platies they can hold:

Tank sizeNumber of platies
5 gallons2 females, no males
10 gallons2-3 females, no males
20 gallons3 females and 1 male
55 gallons6 females and 2 males

As you can see, the number of platies you can keep in a relatively large tank isn’t linear. 

If we stuck to the 1-inch per gallon rule, we could have said that you can keep about 27 platies in a 55-gallon tank, but that is just too much.

Keeping so many platy fish in the same tank will end up in tons of conflicts and harassment. 

That brings us to another rule, which is to avoid keeping more than two to three males in a single tank (unless your tank has a lot of hiding spots).

If you live outside the US, here is a similar table in liters:

Tank sizeNumber of platies
20-30 liters2 females, no males
60 liters2 females and 1 male
75 liters3 females and 1 male
200 liters6 females and 2 males

What Is The Minimum Tank Size For Platies?

The minimum tank size for platies is 10 gallons. Some believe that you can go as low as 5 gallons, however, that will stress your platy fish significantly.

In a 10-gallon tank, you can comfortably accommodate a group of two to three females. However, adding a male to this tank may end up with harassment.

Either way, you shouldn’t keep just one platy in a tank, be it a female or a male.

What If I Add More Platies Than Recommended?

Let’s say that you wish to grow more than four platies, but all you got is a 20-gallon tank or less. Well, it’s certainly possible, but you’re taking a risk in several ways.

First, you can easily overpopulate your tank. The biggest problem in a crowded aquarium is the production of ammonia, which is mainly generated from fish waste and leftovers.

The more fish you have, the higher the risk of an ammonia spike. That will force you to perform more frequent water changes and maintenance.

It is also worth mentioning that ammonia will later turn into nitrite which will turn into nitrate. Any of these compounds can be eaten by algae, which will also take over.

Second, if you have a lot of males, they are very likely to compete with each other for the females. Therefore, if you decide to raise a large group, prefer the females at all costs.

Do Platies Need To Be In Groups?

Platies don’t have to be in groups since they are not schooling fish. However, they will benefit from such conditions, especially in terms of safety, temperament, and reproduction.

Platies are highly social and do better when kept in small groups. All you need to do is set up a tank with the correct number of fish, preferably three females for each male, as mentioned earlier.

Many fish owners wish to grow a single platy fish in a fish tank. That is possible, but it won’t benefit from the advantages a group has to offer.

Can You Keep Just Female Platies?

You can keep just female platies in your tank. That is a common practice among fishkeepers that wish to avoid reproduction. 

Female platies are not aggressive and will coexist peacefully. On the other hand, you shouldn’t keep a fish tank that accommodates mostly or only male platies.

Bear in mind that some female platies will mate with male platies before you buy them from the store.

In other words, they can still give birth to young platies even though the tank doesn’t have any male platies.

  • If you’re not sure how to distinguish between male and female platy fish, here is an excellent video showing how to do that:

How To Setup A Platy Fish Tank

If you want to rear multiple platies, you have to create a conducive environment for them. This means the following:

1. Make Sure That Your Tank Is Fully Cycled

This part is important because you are about to add a relatively large group of fish to your tank, and you run the risk of ammonia and nitrite production.

There are a few steps you should take to ensure your tank is fully cycled:

  • Grab a testing kit and check the water parameters.
  • Make sure that the ammonia and nitrite are at 0 ppm and nitrate is below 20 ppm.
  • Add the platy fish to your tank.
  • Check the water again after five hours and ensure the parameters remain the same.

Cycling allows the tank to nurture beneficial bacteria that can break the ammonia down.[3] If the ammonia concentration in your tank keeps spiking, you did not cycle the tank to completion.

If you are confident that you cycled the tank, you probably undermined your work by either replacing your filter’s biological media or exposing it to chlorine, a substance that can kill the beneficial bacteria in your tank.

Either way, you have to ensure that your tank is cycled correctly. If it isn’t, one solution is to get some filter media from a friend with an older tank. 

The bacteria in their filter media will expedite the cycling process in your tank. You can also get the API Quick Start Nitrifying Bacteria (link to Amazon).

An illustration of the nitrogen cycle that typically takes place in a healthy fish tank environment.

2. Set The Right Water Parameters

These are the ideal water parameters for a platy fish tank:

Temperature70°-80°F (21°-27°C)
General hardness (GH)10-28 dGH (167-467 ppm)
Carbonate hardness (KH)3-5 dKH (54-90 ppm)

Generally, platies are hardy creatures. They can tolerate parameters that are less than ideal. Some people even rear them in soft water. 

However, it would help if you didn’t force them to grow accustomed to the wrong parameters. This will induce stress in the creatures.

You can easily tell that the platies you added are stressed by checking their behavior. For example, some of them might stay at the bottom of the tank. Others will gradually lose their color and turn white.

A stressed platy fish that started to lose some of its colors.

3. Consider Adding A Few Airstones

Avoid filters that create a strong flow. Platies prefer very little water flow. 

They don’t need powerheads, wavemakers, or any other device used to increase the aeration of the tank. 

You have to rely on the filter to ensure that the tank is adequately aerated. However, where necessary, you can add one or two airstones.

These serve a unique purpose as they break the surface tension, allowing CO2 to enter the water. That will help you control algae growth in your tank.

The airstone that I use in my tank is the Hygger Aquarium Air Stone Kit (link to Amazon), mostly because it is extremely quiet.

Besides carbon dioxide, airstone will obviously increase the oxygen in your tank, which is now being consumed even faster.

Platies suffering from a lack of oxygen will frequently swim at the top of the tank. This is a serious red flag.

4. Adjust The Environment

Platies do not have a preference where the substrate is concerned. But they require plants. 

You can fill their tank with hornwort, amazon swords, duckweed, and java moss, to mention but a few. 

The quantity will depend on the type of platy. For instance, southern platies are happiest in loosely arranged tanks. They do not have the same affinity for dense foliage that you may find in other types of platies.[4]

Besides plants, you can also include rocks, caves, pots, and other decorations. But you should avoid items with sharp edges. They may cut into your platies.

Plants and decorations are perfect for community aquariums with large and aggressive fish. 

The plants and decorations will provide hiding places for platies that have attracted the attention of bullies. 

5. Pick The Right Tankmates

Platies are pretty small, and that makes them a target for larger creatures. For that reason, you have to select their tankmates carefully. 

It would be a mistake to assume that every large fish is a bully that cannot coexist peacefully with platies. 

However, because platies are such active swimmers, they are just as likely to antagonize larger, slower-moving, more docile fish. 

You have to match your platies with creatures that are not only peaceful but equally active. 

Some suitable matches include:[5]

  • Mollies
  • Guppies
  • Gouramis
  • Danios
  • Neon tetras
  • Rasboras
  • Cory catfish
  • Bristlenose plecos
  • Rainbowfish

Bad tankmates for platies include: 

  • Swordtails
  • African Cichlids
  • Arowanas
  • Tiger Barbs 


It is essential to consider the tank’s size when adding platies. For the most part, if your tank is about 20 gallons, a group of three females and one male would be ideal.

After picking the group’s size, make sure the water parameters are suitable for platies and that the rest of the fish in your tank can peacefully live with them. 

Lastly, consider the pH, hardness, temperature, ammonia, nitrates, and nitrites before and after introducing the new fish.