How to take care of Black molly fish?

We will talk about black molly fish care in this blog post.We will also discuss important factors such as their habitat, types,lifespan,tank set-up, water parameters and healthcare, etc.Everything you need to know about black molly fish care will be briefly discussed.


In this blog

  • Key specifications of black molly fish
  • Why is black molly fish care important?
  • How many black molly fish should you start with as a newcomer?
  • Habitat of black molly fish
  • Types of black molly fish
  • Different strains or colors of black molly fish
  • General and physical attributes of black molly fish
  • Black molly fish lifespan
  • Black molly fish tank set-up
  • Black molly fish diet and feeding requirements
  • Black molly fish healthcare and health conditions
  • Black molly fish daily care and Bi-weekly care tips
  • Summary

How to take care of Black molly fish?

Daily care tips for black mollies

  • Keep the aquarium walls  clean by wiping it properly everyday.
  • Water should be monitored to check ammonia and nitrate spikes in the tank.
  • Maintain a strict gender ratio of 1 male for 3 females, because females get stressed or die out of stress due to constant mating attempts.
  • Vital parameters should be checked everyday.
  • Feeding should be done in small amounts 2-3 times a day.Don’t overfeed and always eliminate unused food from the tank.
  • Shift sick fish to another tank until they recover completely.
  • Make sure all the tank accessories and equipment are all well fitted and are working properly.

Bi-weekly care tips for black mollies

  • 15-20 % water should be changed once in two weeks to keep the levels of ammonia and nitrates in check.
  • Live food should be quarantined for two weeks before feeding them to avoid any kind of infections.
  • Plant based diets can be given once or twice a day.
  • Filters should be washed once or twice in a month to make the filtration efficient.
  • Plants, substrate and other decorative items should be cleaned once or twice in a month to avoid growth of unwanted bacterias in the tank.

Key specifications of black molly fish

Name Black molly
HabitatCentral AmericaSouth America 
Lifespan3-5 years
Body sizeBody shapeColorSpecial traitSexual dimorphism2.5 to 4 inches in lengthSmooth black bodyJet blackMelanin pigmentYes 
Another namesOnly black molly
Optimum temperatureOptimum pHWater hardness70F-79F7.5-8.211-30 dH
TemperamentBeginner/experienced Peaceful Both levels
Care levelEasy 
Tank size and set-upTank type (Prefered)30 gallons (110 liters)Community planted aquarium
Preferred plants/decorationsAquatic plantsWell decorated
CompatibilityOther molliesLivebearers 
Number of black molly fish species found Only one 
BreedingLivebearers Tank bred

Why is black molly fish care important?

Black mollies are super friendly aquarium fish of the molly family.They are hardy species and easy to care for, but are equally sensitive to bad water chemistry.

Black mollies can’t survive in such poor conditions.So you have to provide them the right conditions for their growth and longevity.

How many black molly fish should you start with as a newcomer?

As a newcomer,when starting a new school,you can get 3-4 black mollies and introduce them together in the same aquarium.Make sure the tank is bigger and spacious for them to move freely and enjoy their own space in the tank.

Male to female ratio should be maintained to avoid harassment and fighting in the tank.

Habitat of black molly fish

  • Water type- Freshwater or brackish
  • Water movement in wild- Slow moving water
  • Origin – Central and South america

Types of black molly fish

  • Only black mollies

Different strains or colors of black molly fish

  • Black mollies are totally black in color from top to toe.

General and physical attributes of black molly fish

  • Black mollies are produced through cross breeding between common mollies in tank settings
  • Size- 2.5 to 4 inches in length
  • Smooth black body with triangular head
  • Fan shaped tail
  • Short fins
  • Sexual dimorphism is prominent

Black molly fish lifespan

Black molly fish have a shorter lifespan between 3-5 years and their longevity depends entirely on how well they are cared for in aquarium settings.

Lifespan depends on:

  • Water chemistry and other vital parameters
  • Genetics
  • Diets 
  • Compatible tank companions

Black molly fish tank set-up

Tank sizeLight intensitySubstrate/decorationWater parametersTemperatureTank plantsTank mates

Tank size for black mollies

You need to provide the right aquarium size for your black molly to live comfortably and happily.

Black mollies are known for their friendly and peaceful temperament, but like any other aquarium fish, they like to have their own personal space or area to relax and breathe.

Smaller spaces or overcrowding could bring stress and other health issues in them.So, never compromise with the tank size.

  • Tank size- 30 gallons
  • Shape of the tank- Narrow tanks are best for black mollies,where they can move freely without any congestion.
  • Swimming zone- They like to swim from the middle to top layer of the tank
  • Filter type-Canister filter (costlier) / hang-on back filters (cheaper and advisable,because it promotes slow water flow in the aquarium setting)
  • Air pumps- Oxygenation 
  • Male to female ratio in the tank – 1:3

Light intensity for black mollies

For lighting in black mollies tank , it is advisable to use artificial lights or sunlight.Tank plants would want sunlight for staying healthy and fresh in the tank.

  • Sunlight, natural source of light
  • Artificial light like LED bulbs etc

Substrate/decoration for black mollies

They usually swim between the middle of the tank to the top level of the tank,so substrates are not so important for black mollies.The only reason to keep a substrate is to benefit the aquatic plants.

Decorations can be done as per your choice.But make sure the decor items are not sharp and edgy,because they can hurt your black mollies.

The most important of all is to clean the gravel substrate and artificial decors from time to time to avoid the growth of bad microorganisms in the tank.This can hinder their growth by polluting the water conditions.

Decors are used to replicate natural habitat conditions in aquarium settings,to make them feel safe and secure.They act as hiding spots, for playing,swimming and sometimes they sleep near those areas.

  • Sandy substrates or gravels
  • Muddy substrates
  • Rock works
  • Cave like decors

Water parameters for black mollies

Water parameters are the main thing to consider in black molly aquariums, because they are sensitive to poor water conditions.

  • Water flow- slow water movement
  • Optimum pH- 7.5-8.2
  • Water hardness- 11-30

Temperature for black mollies

Black mollies are a tropical fish and require an ideal temperature to survive well in aquarium conditions.Temperature plays a vital role in the metabolism of an organism and their overall growth.

So, it is very important to provide the suitable temperature conditions to avoid stress and disease in fish in such artificial habitats.

  • Prefer warm water conditions
  • Optimum temperature-70F-79F
  • Heaters and thermometers can be used to maintain the ideal temperature in aquarium conditions.

Tank plants for black mollies

Black mollies thrive well in heavily planted community tanks.They appreciate that green environment which gives their tank the touch of their natural habitat.

If possible try to get plants which are easy to care for and provide them a good hiding space when they feel overwhelmed.

Clean the tank plants once a week or twice a week to avoid the growth of unwanted microorganisms,which are not beneficial to their overall health.

Suitable tank plants for black mollies:

  • Anubias nana
  • Water wisteria
  • Java moss
  • Java fern
  • Hygrophila 
  • Amazon sword

Tank mates for black mollies

Black mollies are non-disturbing,friendly and peaceful aquarium fish, they can live happily with almost all fish of the same temperament. They do better in well planted community tanks.

Suitable tank-mates for black mollies:

  • Guppies 
  • Gouramis
  • Danios 
  • Female bettas
  • Tetras 
  • Platies
  • Livebearers 
  • Some invertebrates

Black mollies can’t coexist with:

  • Aggressive fish
  • Small sized fish (end up eating them)

Black molly fish diet and feeding requirements

Feeding black mollies is not at all difficult.Being omnivore they accept all kinds of feed.They like to eat and have big appetites,so you should feed them in moderation in order to avoid indigestion or any gastric troubles.

  • High quality flakes 
  • Fresh vegetable based diet-Zucchini, cucumber,spinach,peas etc.Make sure to blanch them before feeding.
  • Live or frozen food-bloodworms, daphnia,brine shrimp
  • Algae based diet- Algae wafers (hikari brand)

Always remember:

  • Quarantine live food at least for 15 days before them.
  • Feed small amounts of food 2-3 times a day.
  • Give them time to finish their bites.
  • Rotate their diets for better nutrition.
  • Don’t overfeed,it could lead to gastric issues.
  • Include a protein rich diet for better growth.
  • Remove uneaten food or leftovers without fail to avoid infections.

Black molly fish healthcare and health conditions

A dirty, uncleaned aquarium can lead to various health conditions in black mollies.

Poor water conditions may cause problems in their gills, which could be an indication for organic pollutants like ammonia and nitrates poisoning.

  • Molly disease (shimmies):Due to poor water chemistry they become less active and display abnormal swimming patterns.
  • Fin or tail rot disease- A bacterial infection with badly worn fins.
  • Dropsy infection- Due to poor water conditions.
  • Velvet-A parasitic infection,can cause breathing issues in black mollies.
  • Ich or white spots on black mollies-A protozoan parasitic infection.

If your black mollies are developing any of the above mentioned infections then shift them to another tank,i.e a hospital tank and maintain the right water parameters there for their recovery.

If still they are not showing any signs of recovery then consult a vet for treatment or medication.


  • Black mollies are excellent beginner fish.
  • Decorate the aquarium with lots of aquatic plants to increase their survival.
  • Sensitive to bad water chemistry,so it’s quite important to house them in a spacious tank, which allows stable conditions.
  • Maintain a strict gender ratio (1 male : 3 females) 

Frequently asked questions on black molly fish care

Can they survive in brackish water conditions?

Black mollies are hardy in nature and can do well in both freshwater and brackish water conditions.Their survival rate decreases only in bad water conditions.

Do they require extraordinary equipment to keep them?

No, they are easy to care for and are low maintenance aquarium fish. All they need is a good filtration system because of their big appetites.

How to know if they are not doing well?

Black mollies are active swimmers like their other cousin’s and by their swimming patterns and activities you will come to know if they are sick or stressed.They won’t show much activity, and will mostly hide behind the branches and avoid eating.