Molly Fish Care: A Complete Guide From Start To Finish

Mollies are beautiful and hardy fish that make great additions to any aquarium. If you’re thinking about getting mollies for your fish tank, there are a few things you need to know about their care.

In this article, we’ll discuss the essentials of Molly fish care and more! So, keep reading to find out everything you need to know!


Mollies are ideal for beginners due to their hardiness and easy care requirements. They’re sociable creatures, and they’re best kept in groups of at least 4-5. For the tank, a 20-gallon setup is minimum, which is horizontal over high. Keep the temperature between 71-82°F and pH levels between 7.5-8.5.

Being omnivorous, mollies enjoy a varied diet that includes plant and animal matter. While tropical fish flakes should be their main meal, supplementing with brine shrimp or bloodworms can provide extra nutrients.

Mollies are generally robust but can be prone to certain diseases if not cared for. It’s crucial to maintain good water quality to help avoid such conditions. With attentive care, mollies can live up to 5 years.

For tank mates, opt for peaceful fish that aren’t prone to fin nipping. Suitable companions include platies, guppies, dwarf gouramis, and corydoras catfish.

The most important thing to remember about mollies is that they’re livebearer’s. So they’re going to breed a lot.

Are Mollies Easy To Keep?

Mollies are easy to care for, making them a popular choice for aquarium enthusiasts of all levels. They are hardy, peaceful, and can live happily in a tank fors everal years with the right care. Providing them with the proper food, warm water, and hiding places will keep them healthy and content.

One reason why mollies are easy to keep is their adaptability. They prefer warm waters, but they can handle various water conditions, which reduces the need for constant adjustments.

Feeding mollies is straightforward too. They’re not picky eaters and will accept a variety of foods, including flakes, pellets, and live or frozen foods. Ensuring they get a balanced diet is essential for their well-being.

Moreover, mollies are relatively easy to breed in captivity. They’re livebearers, meaning they give birth to live fry instead of laying eggs. This simplifies their breeding process and makes it enjoyable to observe their reproductive behavior in a well-maintained tank.

(Mollies are some of the easiest fish you can keep. If you want to know about more, then check out the 15 best fish for beginners!)

NameMolly Care (Poecilia Sphenops)
Cost$2-$4+ Per Fish
OriginSouth America (Mexico, Colombia)
Care LevelEasy
Lifespan3-5 Years
Size4-5 Inches
Tank Size20 Gallons
FeedingFish Flakes, Live Food, Blanched Vegetables
Community Tank Yes
Tank LevelMid Level
PlantsJava Fern, Amazon Sword, Anubias, Java Moss, Water Wisteria
Tank MatesGuppies, Endler’s Livebearers, Platies, Swordtails, Neon Tetras, Zebra Danios, White Cloud Mountain Minnows, Corydoras Catfish, Dwarf Gourami, Bristlenose Plecos
Breeding TypeLivebearer


Mollies are small freshwater fish with a sleek and elongated body. They come in various colors and patterns, including black, white, orange, and even metallic shades. Some molly varieties have vibrant spots or stripes, adding to their overall beauty. 

These fish are known for their colorful and eye-catching look, making them one of the most common choices for fish keepers who want more hues in their tank.


Mollies usually grow to be around 3.5 to 4.5 inches when they are fully grown. But, there are some mollies that can be slightly bigger or smaller, depending on things like their genes, the food they eat, and the conditions of their tank. Despite their size, they’re very active and can make any aquarium look more lively.


Mollies are generally peaceful fish and get along well with other fish. One important thing to know about Mollies is that they like to be with others of their kind. They don’t move together like a school of fish, but they swim in a group, which help them feel safe and comfortable, however, they can get stressed and fearful when they’re alone.

Male mollies can sometimes become aggressive towards each other when competing for territory or mates. However, their aggression is usually not severe, and they can normally live together peacefully in an aquarium that’s well-maintained and has enough space and hiding spots.


The lifespan of mollies can vary depending on the type, but they usually live for 3-5 years. Their lifespan is also affected by their care. Mollies that are well-cared for and live in a healthy environment will typically live longer than those that aren’t. 

So, by providing mollies with the best conditions, you can help them live long and healthy lives.

Mollies Water Parameters

Now let’s go over the water parameters to remember to give your Mollies the best care possible.

Tank Size20 Gallons


Mollies prefer water that is slightly alkaline, with a pH between 7.5 and 8.5. They can handle various pH levels within this range, which makes them versatile.


Mollies like the water to be warm, around 71°F to 82°F. This temperature range keeps them active and feeling good.

Water Hardness

Water hardness is important for Mollies, and it’s good to know that they can tolerate moderate levels. It’s always best to aim for a hardness between 12 and 25 dGH to keep them comfortable.

Tank Size

The recommended tank size for Mollies depends on the type and size of the species. Generally, it’s best to get an aquarium that holds at least 20 gallons of water. 

However, for larger fish, and if you plan to have a community tank, a tank size of 29 to 55 gallons is more suitable. Providing enough space is essential to ensure your Mollies can swim and thrive comfortably. 

Molly Fish Care Sheet

If you want to know about more fish that are just as colorful as mollies then check out this article on the 58 most colorful fish!

What Do Mollies Like In The Wild?

Mollies are native to the freshwater rivers and streams of Central and South America. They’re found in a variety of habitats, including slow-moving rivers, clear streams, and even brackish waters.

The natural habitat of mollies is filled with soft, acidic water with a temperature of 72-78°F. The water is often slightly brackish, with a salinity of 0.5-1.0%. The substrate is typically sand or gravel, and there’s often a lot of vegetation, such as water hyacinths and floating plants.

Mollies are omnivores, and their diet consists of a variety of small insects, crustaceans, and plant matter. They’re also known to eat algae and detritus.

The natural predators of mollies include larger fish, such as piranhas and catfish. They’re also preyed upon by birds and reptiles.

Mollies are an important part of the freshwater ecosystem in Central and South America. They help to control the populations of small insects and crustaceans, and they’re also a food source for other animals.

How To Setup A Tank For Mollies 

Setting up your Mollies’ tank is one of the most exciting parts of caring for them. However, you need to know the right steps to be successful. 

Choose the Right Tank

The first step is to choose the right tank for your mollies. Your tank should be at least 20 gallons in size, and it should have a lid to prevent the fish from jumping out. You should also choose a tank that has a filter and a heater.

Add the Substrate

The next step is to add the substrate to the tank. If you plan on having aquarium plants (which I’d recommend) then you should use aquarium soil or aquarium gravel, however, if not most substrates are going to be okay as mollies never really venture that low.

Fluval Plant and Shrimp Stratum, For Fish Tanks, 4.4 lbs., 12693
  • Fluval Stratum is made of mineral rich volcanic soil

Add Plants

Plants are an important part of any aquarium, and they provide a number of benefits for your Mollies. They help to filter the water, provide hiding places for the fish, and make the tank more attractive. You can choose a variety of plants for your mollies’ tank, such as anubias, java fern, and water wisteria.

Add a Heater

Mollies are tropical fish, so they need a heater to keep the water temperature at a constant 72-78°F. The heater should be placed in the tank so that the water circulates evenly.

Fluval M100 Submersible Heater, 100-Watt Heater for Fish Aquariums up to 30 Gal., A782
  • Aquarium heater that blends into the aquarium environment with built-in reflective technology that mirrors the surrounding colors

Use the Right Filter

A filter is essential for keeping the water in your tank clean and healthy. They’ll remove waste products from the water, as well as any debris or algae. You can choose a variety of filters, such as hang-on-back filters, canister filters, or internal filters.

Marineland Penguin Bio-Wheel Power Filter 150 GPH, Multi-Stage Aquarium Filtration,black
  • WITH ROTATING BIO-WHEEL: Patented Bio-Wheel technology provides excellent wet/dry biological filtration.

Condition the Water

Before you add the fish to the tank, you need to condition the water. This means removing chlorine and chloramine from the water, which can be harmful to the fish. You can do this by using a water conditioner. Simply follow the instructions on your conditioner of choice.

Seachem Prime Fresh and Saltwater Conditioner – Chemical Remover and Detoxifier 250 ml
  • POWERFUL TREATMENT: Seachem Prime is a complete and concentrated conditioner for both freshwater and saltwater fish tanks, working hard to remove chlorine and chloramine.

Slowly Acclimate your Mollies

When adding your mollies to the tank, it’s important to do it slowly to help them acclimate to their new environment. You can do this by placing the fish in a bag filled with water from the tank and floating the bag in the new tank for 15-20 minutes. After acclimation, carefully add your fish to the tank.

Test the Water

It’s important to test the water regularly to make sure that the water parameters are within a safe range for your mollies. You can do this using a water testing kit. The water parameters that you need to test for are ammonia, nitrite, and nitrate.

API FRESHWATER MASTER TEST KIT 800-Test Freshwater Aquarium Water Master Test Kit, White, Single, Multi-colored
  • Contains one (1) API FRESHWATER MASTER TEST KIT 800-Test Freshwater Aquarium Water Master Test Kit, including 7 bottles of testing solutions, 1 color card and 4 tubes with cap

Maintaining the Tank

After setting up your tank, it’s also crucial to do regular water changes to keep the water parameters in your mollies’ tank within a safe range. Preferably, you should do a 25% water change every week. 

(Setting up your first fish tank can be difficult, if you want a step by step guide, as well as to know what beginner mistakes to avoid, then check out this article!)

Do Mollies Prefer Sand Or Gravel?

Mollies don’t have a preference for sand or gravel. They’ll do well in either type of substrate. However, if you’re keeping mollies with other fish that are bottom-feeders, you may want to use sand. This is because sand is less likely to get sucked into the fish’s mouths.

Mollies Male Vs Female

To tell male and female mollies apart, you can take a look at some of their physical differences. 

Anal Fin

The anal fin is one of the most obvious differences between male and female mollies. Male mollies have a long, thin anal fin that’s shaped like a tube. This is called the gonopodium, and it’s used to transfer sperm to the female during mating. 

Meanwhile, female mollies have a fan-shaped anal fin that is wider and rounder.

Body Shape

Male mollies are generally smaller than female mollies. They also have a more slender body shape, with a longer body and a smaller head. On the other hand, female mollies are larger and have a more rounded body shape.


Male mollies are often more brightly colored than female mollies. This is especially true in types of mollies with a lot of variety in colors, such as sailfin mollies and black mollies. Female mollies are usually more muted in color, but they can still be quite colorful.


Male mollies are more aggressive than female mollies. They’ll often chase each other and fight for territory. However, female mollies are more calm and peaceful.

Gravid Spot

Pregnant Female mollies will develop a dark spot near their anal fin. This is called the gravid spot, and it’s a sign that the female is carrying eggs. The gravid spot will become darker and more pronounced as the female gets closer to giving birth.

Mollies Diet

Mollies love to eat a variety of foods both in their natural habitat and in aquariums. In the wild, they’re omnivores, meaning they consume small creatures like invertebrates, algae, and plants.

However, when kept in an aquarium, it’s important to feed them a balanced diet. The main part of their diet can be high-quality flake food, specially made for fish. But, don’t forget that it’s also beneficial to offer them some vegetables for added nutrition.

For their diet in an aquarium, you can provide proteins and vegetables in the form of flakes, pellets, and frozen foods. Occasionally, you also can give them freeze-dried foods like brine shrimp, tubifex, and blood worms to keep their diet diverse and interesting.

TetraMin Plus Tropical Flakes, Cleaner and Clearer Water Formula 7.06 Ounce (Pack of 1)
  • TROPICAL FORMULATION: Highly digestible flake blend for use as staple food for all tropical fish.

Molly Tank Mates 

When choosing tank mates for mollies, it’s important to choose the best fish to ensure peace and happiness in your tank. Here are 10 great choices:

Guppy Fish

Guppies are lively and colorful, making them ideal tank mates for mollies. Their peaceful nature and small size will help create a diverse aquarium!

Guppy Care Sheet

Endler’s Livebearers

Another colorful and small livebearer, Endler’s Livebearers share similar care requirements with mollies, making them an ideal match. Also, these fish won’t cause any conflicts in your tank.

Endler's Livebearers Care Sheet


Peaceful and available in various bold shades, platies are another great choice that come in a whole variety of colors!

Platy care sheet


With their elongated sword-like tails where they got their name from, Swordtails create a beautiful contrast to your mollies. And the best part? They’re generally peaceful and can coexist harmoniously.

Swordtails Care Sheet

Neon Tetras

Though slightly less compatible, neon tetras’ bright colors and schooling behavior make them an attractive addition to mollies’ tanks. Just remember, providing hiding spots for both of them is important.

Neon Tetra Care Sheet

Zebra Danio

Energetic and lively, zebra danios bring more activity to your tank, complementing the more laid-back nature of your Mollies.

Zebra Danio Care Sheet

White Cloud Mountain Minnows

Just like your Mollies, Minnows, especially white cloud mountain minnows, are calm and sociable fish. They’re excellent tankmates for your mollies and help create a lively and active aquarium.

White Cloud Mountain Minnows Care Sheet


Corydoras catfish are bottom-dwellers that help keep the tank clean by scavenging for food scraps. With their cleaning ability, they make great tankmates for your Mollies.

Common Corydoras Care Sheet

Dwarf Gourami

Dwarf gouramis are colorful and non-aggressive fish, making them suitable tank mates for mollies. Their vibrant appearance adds beauty to your Mollies’ aquarium.

Dwarf Gourami Care Sheet

Bristlenose Pleco

Bristlenose plecos are small algae-eating catfish that contribute to your community tank’s cleanliness. Moreover, they can help maintain a well-balanced tank environment.

Bristlenose Plecos Care Sheet

If you want to know about over 50 great community fish, then you need to check out this article!

Molly Fish Tank Mates


When it comes to choosing plants for your Mollies’ aquarium, it’s essential to pick ones that can thrive in the same water conditions and provide suitable hiding spots. Here are five of the best plant options for Mollies:

Java Fern

Java Fern is a popular choice for Mollies’ tanks because it’s easy to care for and can tolerate a wide range of water conditions. It has broad, sturdy leaves that provide excellent hiding spots for your Mollies.

Java Fern Bare Root | Microsorum Pteropus – Low Light Freshwater Aquarium Plant
  • Provide natural resting and hiding places for your smaller fish and invertebrates

Amazon Sword

The Amazon Sword is another excellent choice for Mollies’ aquariums. It has long, sword-shaped leaves that create a lush and natural-looking environment. Mollies appreciate the cover provided by the Amazon Sword, and it adds a beautiful green backdrop to the tank.

Large Amazon Bleheri Sword 18-24 inches Tall | Live Freshwater Aquatic Plant
  • Easy live aquarium plant specie for any freshwater aquarium


Anubias is a hardy and versatile plant that’s well-suited for Mollies’ tanks. It has thick, dark green leaves that are attractive and robust. Like Java Fern, Anubias can be attached to driftwood or rocks, making it easy to position in the tank.

Java Moss

Java Moss is a low-maintenance plant that can add a lush, carpet-like look to your Mollies’ aquarium. It grows easily and provides hiding places for Mollies’ fry (baby fish). Mollies will enjoy swimming around and playing in the dense foliage of Java Moss.

Marcus Fishtanks Java Moss Taxiphyllum Barbieri Easy Live Aquarium Plant – Buy 2 Get 1
  • LIVE AQUARIUM PLANT – 1 Java Moss (Taxiphyllum Barbieri) golf ball size portion

Water Wisteria

Water Wisteria is a fast-growing plant that can add a vibrant touch to your Mollies’ tank. Its feathery, light green leaves provide ample cover and oxygenation. This plant is easy to care for and can help absorb excess nutrients, promoting a healthier aquarium environment.

Water Wisteria – Hygrophila difformis Live Aquarium Plant – 3 Stems
  • Excellent Easy to grow aquarium plant, very nice bright green color, provides good cover for fry and great leaf surface area for shrimp to sit on. You will get 3 stems

Mollies Breeding

Mollies are livebearers, which means that they give birth to live young. They’re relatively easy to breed and can be bred in a home aquarium. In fact, you can normally just leave them to their own devices and they’ll breed! But if you plan on selecting mollies to breed, then here’s what you’ll need to do!

Here are the steps on breeding mollies:

Setting Up a Breeding Tank

The first step is to set up a suitable breeding tank. The breeding tank should be at least 20 gallons, and should have a heater and filter. You can induce spawning by raising the water temperature by a few degrees over a few days.

Adding Live Plants

Next up, add some live plants to your Molly’s breeding tank. These will provide hiding places for the fry, and also help to keep the water quality high.

Adding Mollies to the Breeding Tank

Add a ratio of 2-3 females to 1 male molly to the breeding tank. This will help to ensure that all of the females are able to mate and reproduce without being stressed out by the male mollies.

Feeding the Mollies

Make sure to feed the Mollies a high-quality diet. After all, a good diet will help to keep your mollies healthy and fertile.

Monitoring the Mollies for Signs of Breeding

As you go through the breeding process, don’t forget to monitor your mollies for signs of breeding. Your male mollies will chase the females, and the female will develop a dark spot near her anal fin called a gravid spot.

The Birth of the Fry

Once the female is pregnant, she’ll give birth to live young. The fry will be very small, and will need to be fed baby brine shrimp or crushed flake food. Once the fry are born, you should remove the adults and add them back to their main tank so the fry don’t get eaten.

Caring for the Fry

Make sure to care for the fry for several weeks until they’re large enough to be moved to a larger tank. They’ll need to be fed baby brine shrimp or crushed flake food. However, you can also give them commercial fry food.

How Long Are Molly Fish Pregnant?

Molly fish are livebearers, which means that they give birth to live young. The gestation period for mollies is typically 45-60 days. This means that the female molly will carry the eggs inside her body for about 2 months before giving birth.

What Does A Pregnant Molly Fish Look Like?

To identify a pregnant molly fish, look for certain signs such as a gravid spot behind the anal fin, a swollen belly, increased appetite, seeking warmth, and behavioral changes like becoming more territorial or aggressive. Additionally, some sources mention black spots in the anus area.

Mollies Common Diseases 

These are the most common diseases that can affect Mollies and what you can do to treat them.

DiseaseSymptoms or CausesSuggested Action or Treatment
IchthyophthiriasisWhite spots on body and fins, flashing behaviorTreat with medication containing formalin or malachite green
Fin RotDeterioration or fraying of fins, redness or inflammationImprove water quality, treat with antibiotics if severe
Velvet DiseaseYellow or grayish film on body, loss of appetiteTreat with copper-based medication
DropsySwollen abdomen, protruding scalesIsolate infected fish, treat with antibiotics
ColumnarisCotton-like growth on body or fins, ulcers or soresImprove water quality, treat with antibiotics or antifungals

How Many Mollies Can You Keep Together?

In a 20-gallon tank, you can keep up to four female mollies and two males. This setup helps reduce fighting among the fish because each male can get to two different females for mating. 

So, if you want to keep more than male mollies, you should also increase the number of your female mollies. 

Keeping your mollies in groups is essential for their happiness and well-being, and it’s recommended to have at least four mollies together. Mollies are shoaling fish, so they’re more comfortable living with other Mollies.

How Many Molly Fish In A 5 Gallon Tank?

A 5 gallon tank is too small for mollies. The minimum tank size for mollies is 20 gallons, and even then, it is best to keep no more than 5-6 mollies in a 20 gallon tank. If you have a 5 gallon tank, you can keep a few small fish, such as guppies or a betta.

How Many Molly Fish In A 10 Gallon Tank?

Mollies need a minimum of 20 gallons of water to be comfortable. You can only keep about 1 inch of fish per gallon of water, so in a 10-gallon tank, you can only keep 3 mollies if they’re each 3 inches long. If possible, always go for a bigger tank of 20 gallons or more.

How Many Molly Fish In A 20 Gallon Tank?

The number of mollies that you can keep in a 20 gallon tank depends on the size of the mollies and their activity level. However, a good rule of thumb is to keep no more than 5-6 mollies in a 20 gallon tank.

Facts About Mollies

Here are some unique and interesting facts about mollies that’ll definitely make you love them even more!

  1. Mollies are livebearers, which means they give birth to live, free-swimming fry rather than laying eggs. This unique characteristic makes them fascinating to observe during the birthing process.
  1. Mollies are native to Central and South America and can be found in a variety of habitats, including freshwater, brackish, and even saltwater. This makes them very adaptable fish, and they can be kept in a variety of aquarium setups.
  1. Mollies come in a wide variety of colors and patterns, including black, white, yellow, orange, and even blue. 
  1. Mollies can also be found with different fin types, such as sailfin mollies and balloon mollies. Depending on the species and selective breeding, Mollies can have different fin shapes and sizes. Some have long, flowing fins, while others may exhibit striking patterns on their tails.
  1. Mollies are generally hardy and can tolerate a wide range of water conditions, making them perfect for beginners and experienced fishkeepers 
  1. Mollies are prolific breeders, and in a good environment, they can reproduce quickly. Their ability to give birth to multiple fry in a short period can lead to significant population growth.

What Are The Different Types Of Mollies?

Here are 14 of the most popular types of Mollies found worldwide, along with their descriptions, so you can easily decide which one is best for your aquarium. 

Black Lyretail Molly: Similar to the Black Sailfin Molly but with all-black scales and some white highlights on the fins, Black Lyretail mollies are hardy and peaceful, and they can tolerate various temperatures and a pH level of 7-8.

Creamsicle Sailfin Lyretail Molly: Resembling a creamsicle ice cream with white and gold coloration, Creamsicle Sailfin Lyretail Mollies can thrive in different water conditions.

Dalmatian Molly: Durable and tolerant of varying water temperatures and pH levels, Dalmatian Mollies have black and white markings, just like cute Dalmatian puppies.

Dalmatian Lyretail Molly: Similar to the Dalmatian Molly but whiter in color with small black spots. Dalmatian Lyretail Mollies are hardy and suitable for beginner fish keepers.

Gold Doubloon Molly: Gold Doubloon Mollies are mollies that stand out because of their bright yellow and black colors. These fish need enough swimming space in a tank larger than 30 gallons.

Balloon Belly Molly: Balloon Belly Mollies are friendly fish that have a rounded shape and come in white, black, or yellow with a distinctive lyre-shaped back fin. Also, they prefer an aquarium larger than 30 gallons.

Black Molly (Common Black Molly): The common black molly, also known as the black molly, is a hardy fish that’s also ideal for beginners. They have a mostly black body with spots of various colors. 

Golden Sailfin Molly: The Golden Sailfin Molly is another molly that has a bright, golden color. It thrives in hard water conditions and can grow up to 6 inches in length.

Gold Dust Molly: Resembling the Black Molly but with a rich golden color and short fins, Golden Dust Mollies can reach up to 5 inches long.

Harlequin Sailfin Molly: Extremely attractive with a black and white base and gold speckles, Harlequin Sailfin Mollies are peaceful and grow up to 6 inches long.

Black Sailfin Molly: Black Sailfin Mollies are peaceful fish with long, beautiful, flowing fins. They require a 30-gallon tank and should not be housed with fish that nip fins.

Marble Lyretail Molly: Strikingly attractive with black and white colors, Marble Lyretail mollies need a tank larger than 30 gallons and a small amount of salt in their water.

Platinum Lyretail Molly: Platinum Lyretail Mollies are stunning, featuring a platinum/gold color and tall dorsal fins that can definitely make any tank even more attractive.

White/Silver Sailfin Molly: Great for beginners, White/Silver Sailfin Mollies have silvery-white scales and long fins, reaching a length of 5 inches. Just like Black Sailfin Mollies, they also need a tank bigger than 30 gallons.

Will Mollies Nip Other Fish?

Mollies are generally peaceful fish, but they may nip at the fins of other fish under certain situations. If their tank is overcrowded or has too many male mollies, they might start nipping others to establish a hierarchy or territory. This behavior is more likely to happen when your mollies feel threatened or stressed.

And because they’re very active, they may nibble on things out of curiosity to explore their surroundings. To avoid this behavior, it’s important to choose suitable tank mates and ensure the aquarium is properly sized and maintained. 

If you see your mollies nipping other fish, it’s important to deal with any possible sources of stress or aggression in the tank.

Are Mollies Good Beginner Fish?

If you’re thinking about getting into fishkeeping, mollies are a great place to start. They’re pretty easy to care for, and they come in a wide variety of colors.

Here are some of the reasons why mollies are good beginner fish:

  • Mollies are pretty low-maintenance. You don’t need to have a super fancy aquarium or spend a ton of time on their care.
  • They’re hardy. They can tolerate a wide range of water conditions, so you don’t have to worry too much about keeping things perfect.
  • Mollies are social fish. They like to be around other fish, so it’s a good idea to get at least a few of them for starters.
  • And of course, Mollies are absolutely be. There are so many different colors of mollies, so you can find one that’s perfect for your aquarium.


Here are some more frequently asked questions that people have about taking care of mollies!

Why Is Your Molly Sitting At The Bottom Of The Tank?

When a molly is sitting at the bottom of the tank, it can be a sign of various potential issues. Some common reasons for this behavior include swim bladder infections, stress, illness, bad water conditions, pregnancy, and physical trauma. 

How Big Do Black Molly Fish Get?

Black mollies can reach a maximum length of 3 inches, but typically only grow up to 2 inches. Their size is influenced by factors such as their type, water quality, and diet.

Why Is Your Molly Swimming Upside Down?

When a molly fish is swimming upside down, it is likely experiencing an issue with its swim bladder, also known as swim bladder disease. This can be caused by various factors such as constipation, poor diet, eating habits, infections, or deformation of the swim bladder. 

Can Mollies Live In Tap Water?

Mollies can live in tap water, but it is important to test the water quality before adding them to the tank. The water should be free of chlorine and chloramine, and the pH should be between 7.5 and 8.5.

Do Mollies Clean The Tank?

Mollies don’t really clean the tank. They’re not bottom-feeders, and they don’t eat algae or other debris. Mollies are omnivores, and they need to be fed a diet of flakes, pellets, and live food.


Mollies are a great choice for beginner and experienced fish keepers. With proper care, they can live for many years and bring you years of enjoyment. By following the tips in this care guide, you can ensure that your mollies live long and healthy lives.

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