Molly Fish Care Guide – How to Care for Mollies?

Molly fish are small-sized tropical fish that, as a result of hybridization and selective breeding, are available in a diverse range of colors and specimens.

They can live in both freshwater and brackish water. Mollies are unpretentious fish that I usually recommend as a starter fish for beginners.

That said, I also encourage people to read up on them as much as possible, so they can offer them an environment in which they can thrive.

This molly fish care guide I put together will help you care for mollies and master the particulars of these species. Thus, you will be able to maintain an environment in which your mollies will feel right at home.


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Aquarium Size for Mollies

Aquarium size is crucial for any type of fish, not only mollies. A small, crowded tank is never advisable for any kind of fish, so don’t skimp on investing in an appropriately sized aquarium.

Having an appropriate tank size is important for molly fish, especially if you choose mollies that grow a bit larger, like the sailfin molly.

Generally, molly fish reach sizes of 3 inches for males and up to 4 inches for females.

They’re active fish with a high bio-load, so keeping stable water parameters is easier when you have a roomy tank to work with. I should also mention that mollies breed like crazy, so you should also account for resulting fry when setting up a tank.

Few fry survive, however, since mollies do tend to eat their babies, therefore, there won’t be too many fry to worry about, but you should still factor this in when choosing a tank.

Set up a 25-gallon tank, which can make them feel comfortable and in which you can maintain stable water parameters and can accommodate any potential molly fry.

Mollies enjoy a planted aquarium and you’ll often see them scraping off algae from the plants, since they enjoy feeding on algae in the wild as well.

Female to Male Molly Ratio

Like most livebearers, mollies too are fast breeders and different breeds of mollies can breed among themselves.

You don’t have to worry about them not breeding, in fact, you may end up being worried about just how much they breed.

Because male molly fish incessantly pursue females, it’s best to limit the number of males in a tank when also keeping females. This rule applies to all livebearers.

Never keep a lone female with multiple male mollies. You should follow the one male to three females rule, or even better, avoid mixed-gender tanks if you don’t want them breeding at all.

If you’re looking to keep mollies with other fish in a mixed-species aquarium, opt for peaceful and calm tank mates like guppies, platies, bristlenose plecos, harlequin rasboras, etc.

Water Parameters for Molly Fish

Molly fish are quite adaptive to a variety of tank conditions, which is why they’re categorized as a hardy fish species.

Still, sudden temperature changes or changes in toxin levels should be avoided and you should strive to maintain a stable biotic balance.

1.  Temperature

Molly fish tolerate a wide range of temperatures from 70 °F to 82 °F, or even a bit higher. While there is a lot of range in temperature conditions, sudden changes are not tolerated, therefore, invest in a water heater for your molly fish to maintain stable temperatures in the aquarium.

2.  Water pH and Hardness

Generally, mollies prefer hard water (15-30 dGH) and enjoy higher pH values (7.0-8.0). Always check the preferred pH and hardness range for the molly breed you’re planning to keep as differences between breed preferences do exist.

3.  Salt or No Salt?

I mentioned that molly fish can survive in brackish water too, however, since mollies are mostly kept in mixed-species tanks, you should avoid adding any salt to the water when there are other freshwater fish in the tank.

When mollies are in a species-only tank or quarantined, you can add some salt. Some mollies like the Yucatan molly fish requires brackish water to thrive, but other mollies really don’t need salt in their water.

Therefore, with some molly species, you won’t need to add any salt to the tank and it’s more of a matter of “they tolerate salt, but don’t require it”.

Changing Water for Mollies

While the addition of salt to the water for mollies is a debatable issue, everyone agrees that frequent water changes is a must-do when keeping mollies.

Mollies have a high bio-load, so weekly water changes (25-30% changes) are required to keep the water column clean, eliminate toxins and refresh the water in the tank.

You can buy aquarium water from your pet store, but you can also use tap water for water changes, provided that you:

  • Dechlorinate your water and get rid of heavy metals using a water conditioner (like SeaChem Prime) or if you have a water filter installed in your home that targets these water contaminants;
  • The water you use for water changes has the same temperature and parameters as the water in the tank.

In a tank with more fish, you may need to perform bigger water changes. Monitoring water parameters can give you a good idea of how often and how much water you should replace each time.

Feeding Your Molly Fish

Feeding molly fish is a piece of cake since they’re an omnivorous fish species that accept most foods. In the wild, mollies also consume algae and plant matter, so make sure their diet contains that too.

Feed mollies a good quality flake food and supplement that with live or frozen foods like brine shrimp, tubifex or daphnia.

Mollies also require enough vegetable matter, so find flake foods that also contain vegetable matter, or feed them pieces of boiled veggies like cucumbers, squash, or lettuce leaves.

Since molly fish are very active, they require enough sustenance. You can feed them 2-3 times a day with small amounts they can eat in 3-5 minutes.

Be careful not to overfeed them, because overfeeding causes toxin levels to rise in the aquarium and adversely affect the health of your fish as well.

Molly fish are known to eat more than they need to, so it’s your job to portion their food in a way to ensure they get enough food without overeating.

Water Filtration for Molly Fish Tank

You probably keep reading that molly fish are extremely hardy and adapt well to many tank conditions, so it’s reasonable to ask yourself: Do mollies need a filter?

Although classified as hardy fish, if you want your mollies to have the absolute best conditions, provide them with higher than average water filtration.

A hang on back filter sized accordingly for your tank will work best for keeping the water clean for your mollies.

If you have only a few fish in your tank and you can keep feeding under check, you may get away without using a water filter.

If you opt for a filter-free tank set up, make sure you have plants in the tank, which will help clear some of the toxins.

Make sure you have a thicker substrate too (a thicker substrate can help create an anoxic zone with beneficial bacteria transforming nitrites into nitrogen and oxygen gas), and most importantly perform larger water changes (upwards of 50%) on a regular basis.

Alternatively, if you have an air pump you can set it up with a sponge filter that will help remove ammonia.

That said, I believe having a filter system is the best way to keep the water clean. It’s also less work, but you can do without one if you’re careful with how you stock the tank, cleaning and avoiding overfeeding.

Water Heater for Mollies

Unless you live in a tropical climate, a water heater is something you should absolutely have when housing mollies.

Mollies require water in the 70°F to 82 °F range, which you can’t provide in your home. Therefore, invest in a quality water heater, otherwise you risk exposing your mollies to diseases.

A water heater will also ensure that water temperature is kept stable and sudden drops in temperature are avoided.

Artificial Light for Molly Fish

Artificial lighting is not a must for molly fish, although they do enjoy some well-lit areas in their aquarium.

Generally, mollies will do just fine with the natural light that comes through your window, your live plants, however, will require additional lighting.

Buy a lighting system that offers enough light for your plants to thrive but do stick to a lighting schedule since too much light is not ideal neither for your fish, nor for your plants.


Mollies are a good choice if you want an interesting and beautiful fish species that isn’t too pretentious when it comes to tank conditions and food.

If you know their requirements, you can offer them ideal tank conditions, which will keep them healthy and strong.

Find suitable tank mates for your mollies when keeping them in a mixed-breed aquarium and be careful not to overfeed them.

I hope may molly fish care guide has prepared you for what to expect when keeping mollies and you can set up an aquarium that will meet their needs.

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