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How Many Mollies in a 5 Gallon Tank? (Answered)

One of the most popular freshwater fish is molly. They are very attractive and come in various vibrant colors. They are peace loving and a very easy to care fish. Give them proper food, change water, they can also adjust in small tanks. 

However, they are very sensitive to cleanliness and need minimum space to move and swim freely; otherwise, they easily fall sick and may not survive.

How many mollies in a 5 gallon tank?

Mollies are tiny fishes that can live in small tanks but 5 gallons is too small for them. Depending on the species, 1 inch black male molly can be kept 2 or 3 in a 5-gallon tank, while female black molly should not be kept more than 2. For their longer life, at least a 10 gallon tank will be ideal.

Mollies are free-living fish that thrive in groups or clusters. Therefore, in a 5-gallon tank, it’s best to keep two 1-inch mollies at a time, while other experts recommend only keeping one. However, it also depends on the species and gender of mollies. 

Two-three 1-inch male mollies can be put into the 5 gallon tank with proper filtration and care but females will need more space and water. 

Black mollies: 

Two or three black mollies, mollies of the same gender, and spices can live freely in a 5-gallon tank because these are small kinds of mollies. More than the number, may cause the tank to overflow. Female mollies grow about 1 inch longer than males. 

Therefore, three male mollies can live peacefully in a 5-gallon tank, but two female mollies can find difficulties, so not more than two female black mollies should be kept. 

Mollies produce a lot of waste, so it’s best not to keep more than two at a time, as this will increase the danger of sickness if the water isn’t filtered on a weekly basis. 

In addition, too many mollies in a 5-gallon tank will deplete the oxygen supply and make it difficult for the fish to thrive. 

Balloon mollies: 

These mollies require more space than black mollies, so not more than two mollies are recommended for a 5-gallon tank. Because balloon mollies are restless fish who thrive in open spaces, having too many mollies in a 5-gallon tank will stunt their growth. 

Aside from the fact that female balloon mollies require more space than males, there should not be more than one balloon molly in a 5-gallon tank.

 In general, the tank size is determined by the length of the mollies, so for a two-to-three-inch molly fish, three gallon tank is recommended, as balloon male mollies grow up to that size, so two will fit in a five-gallon tank, but no more than that should be kept.

Can mollies live in a 5 gallon tank?

Mollies are the freshwater fish that love to live with a group. They can live freely in small tanks but less than 10 gallon fish will be too small to survive. Normally, for a group of 4-5 mollies, a 20 gallon tank is necessary for their longer and healthier life. 

However, you can put two 1-inch male mollies in a 5 gallon tank as baby mollies can live pretty well in a small tank. But normally female mollies grow larger than male so, it wouldn’t be ideal to put female mollies in this small tank.

Do mollies need big tanks?

Mollies can live freely in small tanks but the size of the tank depends on the number of fishes and their species. If you want to add at least 4 mollies together as they can live happily for a longer period of time, you should choose a tank that is bigger than 10 gallons. 

Though black mollies can live in little water, if you choose balloon mollies, they will require more space, else they may not survive.

What is the minimum tank size for molly fish?

The minimum tank size for molly fish is 10 gallons, the bigger the better. However, for freely moving and swimming when they grow bigger, 20 gallons is recommended. They can grow up to 4 inches and live a long time if they get proper maintenance and care. 

But if there’s insufficient space for their swim and move, they can get stressed and may not move. The growth and development of their body can hamper and they might fall sick.

Is a 5 gallon tank big enough for mollies?

Mollies are social creatures; live happily if they thrive as a group of minimum 4-5 together. Moreover, to happily live and swim in a group, they require a minimum 30 gallon tank. A 5 gallon tank will be too small for them to live and move peacefully. 

Though you can put two-three 1-inch mollies in a 5 gallon tank, when they grow bigger it’ll be hard for them to breathe and move. They will be aggressive and fight for enough space. In addition, their development will be hampered and they’ll fall sick. 

Here are the circumstances described that they’ll face: 


Insufficient space will cause stress to the mollies. They will not move and swim as much as they used to out of stress. More signs of stress will be noticed like indifference to food, skin problems, fungal infections, gulping air or different behavioral changes. 

Developmental health issues: 

A small tank for mollies will hamper their health and growth. The growth-inhibiting hormone will be produced that’ll not let them grow bigger. They’ll experience atrophied muscles, spinal deformities and other growth and developmental issues.

Ammonia poisoning: 

The level of ammonia easily rises up in small tanks as the amount of water is low. Ammonia affects the mollies by damaging their fins and scales and burning their skin. 


It’s not wise to keep more than two 1-inch mollies in a 5 gallon tank as they will not find enough space to play, hide, move or swim. They will experience shortness of breath and suffocation. 

How to set up and take care of a 5 gallon tank for mollies?

A proper set up can supply adequate oxygen to the molly fish and install a proper filter process to process the mollies’ waste. The 5 gallon container takes up little space, simple to take care of and is easy to transport. 

You can easily and attractively set up the small tank following these steps: 

Start by cleaning:

To set the tank, clean the entire tank with detergent or soap and then use any wiper or towel, making sure there are no dust traps. 


Many substrates can be used to decorate and set the tank, such as sand, pea pebbles, plants, and stones, which can be clearly laid into the tank. 

Some people choose not to use all of these because it may reduce the amount of room available for mollies to thrive. It’s important not to use too much gravel since fish excrement might sink into the deep gravel, allowing germs to develop.

Install the filter and other necessary equipment:

Next, install the necessary equipment, such as the filter that will collect the mollies’ waste, which should be placed towards the back of the tank. 

Then add the necessary clean water at the proper temperature for the molly fish to survive. A large gallon tank normally requires an air pump to ensure optimum oxygenation, but a 5 gallon tank does not. 

Finally, before placing the molly fish, add prime and stability. Wait two days before transferring them to the tank.

Moreover, it’s also important to take care of your fish tank regularly. Mollies must be kept alive and healthy by cleaning and filtering their water on a daily basis. The first thing to remember is to check the water condition and change water at least twice a week. 

Maintain a consistent water temperature of 24 to 27 degrees centrifugal in the tank. Finally, a neutral pH must be maintained, as well as a nitrate level of not more than forty.

Final thoughts

The free-living fish molly can be kept in small tanks with proper care. In a 5 gallon tank, 3 black mollies can live together but maximum 2 balloon mollies can live in such a small tank. Actually, the more, the better; they can live and swim more happily if the tank size is at least 10 gallons.