Molly Fish Care Guide: Tank Setup, Feeding, Breeding & More

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I really enjoy raising molly fish, I admit. They are incredibly beautiful and pretty easy to care for. It is pretty easy to breed them too.

However, when I was still new to this hobby, I had many questions regarding that species. If you are new to molly fish, this is the place for you.

Here, I will cover everything you need to know from start to finish, so you leave as an expert. So, without further ado, let’s get started.

Molly Fish: Quick Overview

Molly fish (Poecilia sphenops) are a popular freshwater species often found in aquariums, suitable for beginners and seasoned aquarists alike due to their adaptability and peaceful nature.

They are found in slow-moving tropical rivers in North and South America and come in a wide variety of colors and species due to extensive cross-breeding.

Mollies have a flattened body with a triangular-shaped head, with distinct physical differences between males and females.

Males are smaller and have a pointy anal fin, whereas females have a broad and fanned anal fin, and many bear a visible gravid spot, indicating pregnancy.

The average lifespan of a molly fish is three to five years, and their size ranges from four to six inches, depending on the variety, with sailfin varieties often reaching five or six inches.

Also Read: 15 Things You Should Know About Molly Fish

Common Types Of Molly Fish

Before diving into caring for molly fish, allow me to briefly discuss a few common species of molly fish:

1. Sailfin Molly

The Sailfin Molly, draped in hues of black and silver, turns heads with its long, flowing fins. 

This friendly and sturdy fish, which can grow to an impressive 5 inches, loves roomy, oxygen-rich water habitats full of live plants.

It’s important to keep them safe from any fin-nipping tank buddies.

2. Dalmatian Molly

Just like the distinctive dog breed, the Dalmatian Molly is tough and sports a unique black and white pattern.

This fish, which can reach a length of 4.75 inches, prefers a spacious and oxygen-rich tank with live plants where it can freely swim and explore.

3. Black Molly

The Black Molly, with its signature black scales, is a peaceful and robust fish that fits perfectly into community tanks with lots of space and plant life.

This sociable swimmer can grow up to 3 inches, appreciates a varied diet, and loves to share its space with peaceful tank mates of a similar size.

4. Lyretail Molly

The ‘Lyretail Molly’ label covers a range of color variations, including the Dalmatian Lyretail Molly and the Black Lyretail Molly, all sporting a lyre-shaped tail fin.

This friendly omnivore can grow up to 5 inches and enjoys a diet of flake, frozen, and freeze-dried foods, provided the water conditions are stable.

5. Balloon Molly

With a shape that’s reminiscent of a balloon (arched back and round belly), the Balloon Molly comes in a variety of colors including yellow, white, and black.

This fish, which can grow to 3 inches, prefers a plant-rich environment and a varied diet of meaty foods and algae.

How To Care For Molly Fish

Here is a complete roundup of how to care for mollies, starting with their tank setup:

Molly Fish Tank Setup

Let’s start by setting up your molly fish tank correctly:

1. Tank Size

Molly fish are sprightly swimmers that reach a decent size, and therefore need a roomy tank. 

Cramped tanks can stress them out, promoting poor health due to substandard water conditions and insufficient room for movement:

  • Ideal Volume: Molly fish thrive in a tank of at least 20 gallons, which provides enough room for swimming and socializing.
  • Stocking Guide: Typically, you should allocate 2 gallons of water per 1 inch of fish. Keep in mind that adult molly fish can grow up to 4-5 inches.
  • Social Considerations: Molly fish are social creatures and like to live in groups. More fish means you’ll need extra room.
  • Planning Ahead: If you’re starting with young molly fish, bear in mind their growth potential when selecting your tank.

2. Temperature

Being tropical species, molly fish need warm water to survive. It’s critical to avoid abrupt temperature changes as they can induce stress and reduce the fish’s immunity:

  • Optimum Temperature: Keep the tank’s water temperature between 72°F and 78°F (22-26°C) for molly fish to flourish.
  • Location: Avoid placing the tank in areas with drastic temperature shifts, like near AC vents, heaters, or sunlit windows.
  • Temperature Check: Use a reliable aquarium thermometer to keep an eye on the temperature.
  • Acclimation: When adding new molly fish to the tank, let them adjust to the new temperature over a few hours to avoid shock.

3. Water Acidity

Molly fish feel most at home in slightly alkaline water, resembling their natural environment. Regular monitoring and adjusting of pH levels will make your molly fish comfortable:

  • Ideal pH: Molly fish prefer a tank water pH between 7.5 and 8.5.
  • Routine Testing: Checking the pH levels regularly ensures a stable environment.
  • pH Adjustment: Commercial products are available to tweak the pH if required.
  • Natural Remedies: Certain rocks and substrates can naturally balance the pH in your tank.

4. Ammonia, Nitrite, Nitrate

Keeping tabs on ammonia, nitrite, and nitrate levels is crucial as excessive amounts can be lethal to molly fish. Regular testing helps to keep these detrimental chemicals in check.

Here is what you should know:

  • Tolerance: Molly fish cannot endure any ammonia or nitrites; maintain their levels at 0ppm.
  • Nitrate Amounts: Keep nitrates under 20ppm, ideally even below 10ppm, for the wellbeing of molly fish.
  • Routine Check-ups: Weekly testing with an aquarium test kit is advised. I personally use the API FRESHWATER MASTER TEST (link to Amazon).
  • Water Changes: Change the water regularly to control nitrate levels and get rid of any potential ammonia or nitrite.

5. Heater

As tropical species, molly fish need a heater to maintain the right water temperature. A good heater ensures a consistent temperature spectrum:

  • Appropriate Heater: Choose a heater that fits your tank’s volume. A rough guide is 5 watts per gallon of water. My recommendation: Orlushy Submersible Aquarium Heater (link to Amazon).
  • Consistency: A thermostat-regulated heater will maintain a steady temperature.
  • Placement: Position the heater near the water current to spread heat uniformly for your molly fish.
  • Safety Precautions: A heater guard prevents your molly fish from accidental burns.

6. Air Pump, Bubbler

Air pumps and bubblers enrich the tank with oxygen and aid water circulation. This is essential for molly fish, who thrive in well-oxygenated water.

Here is a brief explanation:

  • Oxygenation: Air pumps and bubblers ramp up oxygen levels, crucial for molly fish health. My recommendation: Hygger Aquarium Air Stone (link to Amazon).
  • Water Flow: These devices help in distributing heat and nutrients evenly across the tank.
  • Stimulation: Bubbles create a stimulating environment for molly fish.
  • Emergency Preparedness: During power cuts, an air pump can keep providing oxygen, saving your molly fish.

7. Filter

Top-notch filtration is critical for preserving water purity and warding off toxins. Molly fish thrive in pristine water, something a good filter can help achieve:

  • Adequate Filtration: Choose a filter with a rating for at least 1.5-2 times your tank’s volume to ensure molly fish enjoy a pure living space. My pick is the Fluval C4 Power Filter (link to Amazon).
  • Biological Filtration: The presence of beneficial bacteria that counteract harmful chemicals plays a major role in molly fish health.
  • Mechanical Filtration: This feature works to eliminate larger waste particles from the water, ensuring a hygienic home for molly fish.
  • Chemical Filtration: This can be useful in eliminating medicines, tannins, and other potential toxins from the water.

8. Plants

Live plants provide molly fish with hideouts, help reduce stress, and boost water quality. They also echo the molly fish’s natural living conditions.

Here are a few points to consider:

  • Haven Spots: Plants serve as safe retreats for molly fish, reducing stress levels.
  • Water Clarity: Plants soak up harmful nitrates, enhancing water circumstances for molly fish.
  • Nature-Like Ambiance: Incorporating plants replicates the molly fish’s natural environment, promoting their natural behavior.
  • Plant Preferences: Resilient, easy-maintenance plants like Java Fern or Anubias are ideal for a molly fish aquarium.

9. Light

Correct lighting is essential in mimicking a natural day-night pattern and boosting plant growth. While molly fish aren’t dependent on special lighting, it boosts their overall wellness:

  • Day-Night Sequence: Stick to a steady lighting schedule (roughly 8-12 hours of light) to replicate natural daylight patterns for molly fish.
  • Plant Growth: Sufficient lighting encourages plant growth, enriching the habitat for molly fish.
  • LED Lights: These are power-saving and produce less heat, which could impact the aquarium’s temperature for molly fish. My recommendation: Hygger Full Spectrum Aquarium Light (link to Amazon).
  • Sunlight Alert: Direct sunlight can lead to temperature surges and algae proliferation, both harmful to the molly fish’s environment.

Also Read: Molly Fish Tank Setup

How To Feed Molly Fish

When you’re feeding molly fish, remember three key aspects: the type of food, the quantity, and the feeding frequency:

1. What Do Mollies Eat?

Molly fish have an omnivorous diet; they enjoy both plant-based and animal-based foods.

In the wild, they munch on algae, plant materials, small invertebrates, and even fish fry occasionally:

  • Store-bought Foods: Consider top-quality flake or pellet foods as your go-to source of nutrition for molly fish. My recommendation: API TROPICAL PELLETS (link to Amazon).
  • Veggies: Mollies have a taste for blanched veggies like peas, spinach, and zucchini. Supplementing their diet with such vegetables can help replicate their natural food sources.
  • Protein: You can occasionally offer live or frozen food items like brine shrimp, bloodworms, or daphnia to molly fish as a tasty treat.
  • Algae: Foods that contain algae, like spirulina flakes or tablets, are great dietary additions for molly fish, who naturally graze on algae.

2. How Much Do Mollies Eat?

Mollies should be fed only as much as they can gobble up within a few minutes.

Overfeeding can lead to weight issues and other health problems, as well as degrade the quality of the water.

Here are a few points to consider:

  • Feeding Guideline: As a rule of thumb, feed your molly fish only what they can eat in 2-3 minutes.
  • Watchful Feeding: Keep an eye on your mollies during meal times to ensure they’re eating without leaving behind any leftovers.
  • Avoid Overfeeding: Overfeeding can result in obesity, health complications, and unsuitable water conditions for mollies.
  • Clean Up After Meals: Make sure to remove any leftover food post-feeding to stop it from decomposing and polluting the water.

3. How Often Do Mollies Eat?

It’s healthier for your mollies to have several small meals throughout the day rather than one large feeding.

This routine mirrors their natural feeding pattern and can support their overall wellbeing. Here’s what you should do:

  • Regular Feedings: Provide your molly fish with 2-3 small meals each day.
  • Routine Matters: Maintain a regular feeding routine so your molly fish can anticipate meal times.
  • Varied Diet: Don’t feel obligated to stick to the same food at each feeding. Alternate between different food types for a more balanced diet.
  • Consistent Feeding: While some species of fish do well with a weekly fasting day, mollies thrive on a consistent feeding schedule.

Also Read: How To Feed Molly Fish

How To Pick Tank Mates For Molly Fish

Choosing tank mates for molly fish involves finding species that prefer similar water conditions and have compatible temperaments.

Ideally, tank mates should be peaceful community fish that won’t nip at the mollies or compete too aggressively for food.

Here are a few points to keep in mind:

  • Similar Environment Needs: Choose tank mates like platies, guppies, or swordtails that thrive in the same water conditions as molly fish.
  • Peaceful Temperament: Avoid aggressive or fin-nipping species; tetras, danios, and certain types of gouramis can live harmoniously with molly fish.
  • Size Considerations: Avoid larger, predatory fish that could see molly fish as food. Fish of similar size are generally better companions.
  • Dietary Needs: Make sure the tank mates you choose have similar dietary needs to molly fish, to ensure all species get their nutritional requirements.
  • Activity Level: Species with similar activity levels, such as other livebearers or smaller species of catfish, make excellent companions for molly fish.

Here is the full list of species that, in my opinion, are considered peaceful and can be kept with molly fish:

  • Neon Tetra (Paracheirodon innesi)
  • Cherry Barb (Puntius titteya)
  • Corydoras Catfish (Corydoras spp.)
  • Guppy (Poecilia reticulata)
  • Platy (Xiphophorus maculatus)
  • Harlequin Rasbora (Trigonostigma heteromorpha)
  • Swordtail (Xiphophorus hellerii)
  • Zebra Danio (Danio rerio)
  • Bristlenose Pleco (Ancistrus sp.)
  • Kuhli Loach (Pangio kuhlii)

On the other hand, I would avoid aggressive fish that will likely harass your mollies. Here is my full list:

  • Tiger Barb (Puntigrus tetrazona)
  • Red-Tailed Shark (Epalzeorhynchos bicolor)
  • Jack Dempsey Cichlid (Rocio octofasciata)
  • Green Terror Cichlid (Andinoacara rivulatus)
  • Convict Cichlid (Amatitlania nigrofasciata)
  • African Cichlids (Various species from the Cichlidae family)
  • Oscar (Astronotus ocellatus)
  • Rainbow Shark (Epalzeorhynchos frenatum)
  • Jewel Cichlid (Hemichromis bimaculatus)
  • Betta Fish (Betta splendens)

Also Read: 19 Great Molly Fish Tank Mates

How To Breed Molly Fish

Breeding molly fish is a direct process since they are livebearers, signifying that the female gives birth to fully developed fry instead of laying eggs.

It requires the right environment, an ideal male to female ratio, and suitable care for the fry. Here is a brief overview:

  • Tank Preparation: Design a separate breeding tank replicating the preferred conditions for molly fish: warm, slightly alkaline water, abundant with plants or hiding places.
  • Population Ratio: Populate your breeding tank with molly fish, ideally maintaining a ratio of one male to every two or three females to avoid stressing the females with excessive male interest.
  • Nutritional Support: Provide a varied, high-quality diet to promote the health and breeding readiness of molly fish. Incorporate high-protein foods like brine shrimp or bloodworms.
  • Pregnancy Indicators: Keep an eye on your molly fish for pregnancy signs, such as a distended belly and a dark gravid spot near the female’s anal fin.
  • Getting Ready for Birth: As the birthing time draws near, you might choose to place the expectant female in a separate breeding compartment within the tank to secure the fry, or create abundant hiding nooks in the breeding tank.
  • Caring for Fry: After the fry are born, it’s essential to isolate the parent molly fish to keep them from eating the fry, or provide sufficient hideaways for the fry inside the tank.
  • Feeding the Fry: Feed the fry multiple times per day with protein-rich food such as finely ground flake food, infant brine shrimp, or specialized fry food.

Also Read: How To Breed Molly Fish

Guidelines For Pregnant Molly Fish Care

Caring for a pregnant molly fish requires a tranquil setting, a balanced diet rich in nutrients, and close observation for signs of labor.

Post-birth, it’s vital to move the mother away from the fry to avert potential cannibalism.

Here are a few steps to follow:

  • Minimizing Stress: Diminish stress for your expectant molly fish by maintaining a peaceful tank atmosphere, and sidestepping sudden shifts in light or water parameters.
  • Dietary Requirements: Serve your pregnant molly fish a diet abundant in proteins and vitamins to feed both her and the developing fry.
  • Signs of Labor: Be alert for labor indications such as irregular swimming or hiding. These actions hint that birth is on the horizon.
  • Post-birth Separation: Post-birth, relocate the mother molly fish back to the general tank to prevent her from consuming the fry.
  • Health Checks: Monitor the health of the mother molly fish after birth, looking out for symptoms of stress or illness and sticking to consistent feeding and tank sanitation schedules.

Also Read: Pregnant Molly Fish 101

Guidelines For Molly Fish Fry Care

Once the molly fish fry are born, appropriate care includes a diet high in nutrients, optimum water settings, and safeguarding them from predators.

The aim is to rear them until they’re big enough to safely integrate into the main tank:

  • Feeding: Offer molly fish fry several meals a day with high-quality, protein-filled food suitable for their size, such as crushed flake food or baby brine shrimp.
  • Water Condition: Maintain prime water quality in the fry tank, conduct regular water changes, and monitor for suitable temperature and pH levels.
  • Safety: Supply ample hiding spaces for molly fish fry, including dense plantings or specialized fry hideouts.
  • Growth Tracking: Observe the growth of your molly fish fry, ensuring they are developing at a healthy rate and displaying no signs of illness or stress.
  • Slow Introduction: Gradually introduce the molly fish fry to the main tank after they have reached an adequate size, making sure the other fish have become familiar with their presence before releasing them completely.

Also Read: Molly Fry 101

Common Molly Fish Diseases

Like all other fish, mollies can fall victim to various diseases. Here, I will address some of the most common ones:

1. Ich (Ichthyophthirius multifiliis)

Ich is a prevalent parasitic disease in aquarium fish, including molly fish, often displayed by white spots that resemble grains of salt on the fish’s skin.

Timely detection and treatment are vital for successful recovery:

  • Identifying Symptoms: Look out for white spots, clamped fins, loss of appetite, and strange behavior in your molly fish.
  • Isolate Sick Fish: Quarantine the sick molly fish to prevent the parasite from spreading.
  • Temperature Increase: Gradually raise the tank’s temperature to accelerate the parasite’s life cycle, making it more vulnerable to treatment.
  • Medication: Apply a commercial ich medication as directed on the packaging. My recommendation: Fritz Mardel (link to Amazon).
  • Recovery Monitoring: Vigilantly watch your molly fish during and after treatment to ensure full recovery and prevent recurrence.

2. Fin Rot

Fin rot, a bacterial or fungal ailment, leads to a molly fish’s fins fraying or breaking down. Usually, subpar water conditions or injuries trigger it:

  • Recognizing Symptoms: Look for discolored, tattered, or missing fins on your molly fish.
  • Boosting Water Quality: Regularly refresh the water and uphold good filtration, as fin rot is often linked to bad water conditions.
  • Segregation and Treatment: Isolate the affected molly fish and administer appropriate antibacterial or antifungal drugs.
  • Dietary Considerations: Make sure your molly fish gets a balanced diet to strengthen its immunity.
  • Managing Stress: Spot and remove any possible stressors, such as aggressive tank mates, to protect your molly fish’s immunity.

3. Columnaris

Columnaris is a bacterial condition that manifests as white or gray spots on a molly fish’s skin, mouth, and fins. This highly contagious disease can be lethal if not promptly treated:

  • Symptom Surveillance: Be on the lookout for white or gray spots, frayed fins, or ulcers on your molly fish.
  • Fish Segregation: Separate the infected molly fish to prevent the disease from spreading.
  • Medical Intervention: Administer a suitable antibiotic, like kanamycin or erythromycin, to fight the infection.
  • Upholding Water Quality: Ensure optimal water conditions, as columnaris thrives in poor water environments.
  • Monitoring Recovery: Keep a close eye on your molly fish during treatment and recovery to prevent any recurrence of the disease.

4. Swim Bladder Disease

Swim bladder disease impairs a molly fish’s buoyancy, causing unusual swimming or difficulty maintaining an upright position.

It’s often due to overfeeding, constipation, or deficient water quality:

  • Symptom Identification: Look for a molly fish struggling to swim, floating upside down, or swimming at weird angles.
  • Dietary Changes: If overfeeding or constipation is the issue, provide peas or a customized diet to your molly fish.
  • Enhancing Water Quality: Ensure optimal water conditions as poor environments can lead to swim bladder issues.
  • Reducing Stress: Mitigate tank stressors that might be causing the issue, such as hostile tank mates or overcrowding.
  • Expert Advice: If symptoms continue, consult a fish vet for possible medical treatments.

5. Popeye Disease

Popeye disease, or exophthalmia, leads to abnormal eye bulging in a molly fish, often caused by injury, infection, or subpar water conditions:

  • Spotting Symptoms: Check if one or both of your molly fish’s eyes are unusually protruding.
  • Improving Water Quality: Sustain ideal water conditions, as substandard water quality can induce popeye disease.
  • Isolation and Treatment: Separate the affected molly fish and administer an appropriate antibiotic to fight any potential bacterial infection.
  • Handling Injury: If an injury is the cause, ensure sharp decorations are removed or tank mates aren’t bothering your molly fish.
  • Monitoring Recovery: Watch your molly fish’s recovery closely, as a bulging eye may take weeks to heal. If the condition doesn’t improve or worsens, consult a fish vet.

Also Read: 15 Molly Fish Diseases & Their Treatments

Identifying And Treating Stressed Mollies

Spotting symptoms of stress in molly fish is essential for their health and survival. These symptoms may include:

  • Breathing Difficulty: When a molly fish frequently comes to the surface appearing to gasp for air, this could point to stress or inadequate water conditions.
  • Seclusion: Molly fish are usually sociable and active. Increased seclusion might suggest a state of stress.
  • Decreased Appetite: A molly fish refusing to eat or consuming less food than it usually does could denote stress.
  • Faded Colors: Molly fish are recognized for their bright hues. If they exhibit faded colors or lose their distinct vibrancy, it might be a stress-related sign.
  • Unusual Swimming: Noticing your molly fish darting erratically around the aquarium could indicate stress.

Here are some strategies to manage stress in molly fish:

  • Keep the Temperature Just Right: Keep your aquarium’s temperature in the molly fish’s happy range (75-80°F, or 24-27°C). If the temperature swings too much, it can stress out your fish.
  • Feed Them Well: Make sure molly fish get a tasty and balanced diet. Feeding them too much or too little can mess up the water or make them undernourished, causing stress.
  • Give Them Places to Hide: Add some more plants or cool decorations to the tank. These little touches provide hiding spots for molly fish, making them feel safe and less stressed.
  • Keep It Quiet: Put the aquarium in a quiet place since molly fish don’t like loud noises and vibrations.
  • Handle Aggressive Companions: If one molly fish is being picked on by a more aggressive tank mate, you might need to give the troublemaker a time-out.
  • Don’t Overcrowd: Molly fish like their space. Aim to have at least 1 gallon of water for each inch of molly fish, but think about a bigger tank for happier, healthier fish.

Also Read: Stress In Molly Fish


Taking care of molly fish isn’t too tricky. These little guys are tough and can put up with different conditions.

But it’s still good to know the basics, like who they should share their tank with, what to feed them, and how to set up their home right from the start.

And if you notice any signs that they might be stressed or feeling under the weather, and you’re not quite sure what to do, don’t think twice about calling a vet.