The Ultimate Molly Fish Care Guide


Mollies are energetic swimmers that bring color and life to any tank. They’re not too small, they’re hardy, and there’s so many to choose from! Today, we’re giving you Molly fish information so you can take care of these beauties successfully.

Types Of Mollies

The Molly is a livebearing species from the family Poeciliidae. They belong to the same genus (Poecilia) that includes Guppies and Endlers.

There are many varieties and colors of Mollies as brought about by generations of selective breeding.

The main two types are Shortfin and Sailfin Mollies. Shortfins are more common, while Sailfins are bigger and have distinct dorsal fins. We’ve listed some of the most popular ones along with brief descriptions below.

StrainDescriptionColor
Shortfin MollyKnown as the “Common Molly”Black, gold, white, orange/yellow, silver, spotted (Dalmatian Molly), gold and black (Gold Doubloon Molly)
Sailfin MollySlightly bigger and more aggressive, with long sail-like finsBlack, gold, yellow, black and white spotted fins (Harlequin Molly), green
Balloon MollyRound bellyWhite, black, yellow, deep orange, silver, gold
Lyretail MollyKnown for their lyre-shaped tails and long fins; grows to about 5 inchesBlack, black with white highlights, marble, platinum, white, silver
Dwarf MollySmallest of all types at less than 2 inches mature sizeSilvery-gold, gray

Wild-caught Mollies are less colorful and are often gray or silvery-gray in color. They are usually found in the warm waters of the southern US and Central America.

Tank Requirements For Mollies

Livebearers, like Mollies, are best kept with a ratio of 1 male to 2 to 3 females. This is to lessen the incidence of males chasing females as there are more than enough to go around.

Since Mollies grow from 2 to 5 inches (depending on the breed), a group of around 6 Mollies would need a 20 to 29-gallon tank minimum. If you’re considering putting them with other fish, a 55-gallon would suffice depending on the tank mates.

If you’re planning on putting a sponge filter in a Molly tank, you would need at least two as one won’t suffice. A hang-on back filter or something more powerful should do better as Mollies are known to create a lot of waste.

Molly Swimming Up
Molly Swimming Up

While most freshwater fish prefer acidic water, Mollies are quite different in that they like water with a higher pH.

But before you adjust your water to alkaline, it’s best to ask your fish source (pet store or friend) if they were bred locally or if they were imported from overseas. Why? Because imported Mollies are raised in brackish water, therefore, requiring you to do so, too at least in the beginning. You should mimic the salinity of the water they were taken from to avoid shocking the fish.

Imported Mollies should be kept in water with a tablespoon of Aquarium salt for every gallon. But you can adjust this as time goes by. Add less salt for each weekly water change until your Mollies are living in virtually salt-free water. Just make sure the change is not drastic and that your Mollies are not showing any adverse effects.

If your Mollies were sourced from local breeders, you can do away with the salt. Test your water first so you know how much you need to raise the pH level. You can use crushed coral or dolomite for your substrate. You can even use these as filter media.

It would be best if you establish a steady and correct pH level before you put the fish into your tank.

Water ParametersRange
Temperature72 to 78°F (22 to 25°C)
pH Level7.5 to 8.2
Ammonia0 ppm
Nitrates0 ppm
Nitrites< 40 ppm
Water hardness15 to 30 KH
Life expectancy5 years average

Aquatic plants, such as Hornwort, Bacopa, Java Fern, and Java Moss are beneficial in a Molly tank. Aside from the natural filtration and oxygenation they provide, plants give the fish (especially the fry) spaces to hide, play, and graze.

Feeding Mollies

One of the keys to great Molly care is proper feeding.

Mollies are omnivorous, eating flake food, brine shrimp, tubifex worms, bloodworms, and algae.

Vegetables are important for Mollies, as we discuss in our post “Do Mollies Really Eat Algae?”. Just like in humans, vegetables help omnivorous fish— including Mollies— to digest and pass their food properly. So be sure to include some algae wafers or cut up veggies (cucumber, zucchini, lettuce) once in a while into their diet especially if your aquarium barely has any algae in it.

Sailfin Molly
Sailfin Molly Fish

Mollies are fed only once or twice a day in amounts they can fully consume within a minute. If they’re taking too long to finish, you probably gave them too much. As with other fish, abstaining from food once or twice a week will help them keep their digestive systems running smoothly.

Molly Fish Behavior

Mollies are not schooling fish. They won’t die if they’re kept alone or in fewer numbers, but they do feel and look livelier in a big group.

Mollies are livebearers that can sometimes show dominance because of their high energy and urge to mate.

This is evident in their behavior. If you want to know more about this dominant attitude, read “Are Mollies Aggressive With Their Tank Mates?”.

One of the characteristics of male Mollies (and other livebearers) is to fight for the right to breed. Therefore, some scuffling may occur until an alpha emerges and is chosen by the female. This behavior helps create stronger offspring.

But generally, Mollies are great tank mates for a lot of other freshwater (and even brackish water) fish.

Since they’re prolific swimmers, you can’t keep them in a fishbowl. Even if you’re taking care of just one Molly, fishbowls are still not an appropriate habitat. To know why, click on our article “Can A Black Molly Live in a Bowl?

Compatible Tankmates For Molly

Because of the behavior we discussed above, Mollies will do well with a lot of other species, especially ones that are close to their size. Mollies can also adjust to softer water in time as long as it’s not too radical to their comfort zone.

Some compatible tank mates for the Molly are:

  • Tetras
  • Danios
  • Platies
  • Corydoras
  • Angelfish
  • Swordtails
  • Endlers
  • Gouramis
  • Minnows
  • Shrimp
  • Snails

Since GloFish can be any of 5 current species of freshwater fish, not all of them can live with Mollies. To know which ones are okay to keep with these fish, try reading “Can Glofish Live With Mollies?”.

In the case of Guppies, we didn’t put them on the list because there is always the risk of interbreeding. Having “Muppy” hybrids are discouraged in the hobby as they are sterile and, as some put it, unnatural. However, if you have high numbers of both species in both genders, the risk of interbreeding is low.

Because of their energy and outgoing personality, Mollies are great dither fish for shy or aggressive species.

The higher pH level that Mollies enjoy makes them compatible with other freshwater species with the same requirements such as Cichlids, but not all of them. Size-wise and behavior-wise, there are still restrictions. Please click on our article “Can Molly and Cichlids Live Together?” to know which ones you can keep with Mollies. Although they can hold their own, not all Cichlids will tolerate the energetic Mollies in their tank.

What About Balloon Mollies?

Controversy surrounds the Balloon Molly as it is specifically bred with a genetic defect, causing its spine to curve. The result is a “fatter” looking Molly with rounded bellies and slower movements.

Balloon Molly
Balloon Molly FIsh

Balloon Mollies come in several varieties. There’s the Dalmatian Balloon Molly, the Red Balloon Molly, the Lyretail Balloon Molly, and more. They grow to an average of 3 inches long.

Balloon Mollies like larger tanks, so a group of 6 should have a 29-gallon tank at least.

All of these variants of the Balloon Molly are not as fast as other types of Mollies. Therefore, Balloon Mollies are best kept in a species only tank. Don’t worry, you can keep different colors of Balloon Mollies together if you like variety.

While some people see them as adorable, others discourage buying them to discourage further breeding. It is said that the unnatural curve of their spine also limits the full growth of their internal organs. Some argue that these fish are in pain and have lower immune systems as evidenced by their shorter lifespans. One thing is for sure, though, Balloon Mollies are out there and continue to be sold by breeders and pet stores.

Breeding Mollies

Like any livebearer, creating batches of Molly fry is easy.

If you’re interested in breeding Mollies, know that livebearers will always multiply quickly even without help. Mollies are labeled invasive because of this.

Shortfin Mollies can give birth to 40 to 100 babies every 30 days, while the larger Sailfin Mollies gestate for 60 days. You’ll know a female is pregnant by the swollen belly and gravid spot near the anal fin.

Mollies typically eat their young, so not many survive if you keep everyone in a community tank. Females are usually separated before they give birth in a breeding tank. This is done to preserve the fry and give the mother some time to rest before she’s chased by males again.

On the other hand, too much breeding may become a problem for you. To help you out, we have important information in “Mollies Keep Having Babies? Here’s What to Do” you can read. It will be helpful to decide beforehand how you want to keep your Mollies or keep dealing with babies. We also discuss in there some important breeding facts about Mollies.

Molly Fish Fries
Molly Fish Fries

One of the tips we gave there is to keep only one gender of Molly and to get them while they’re juveniles. You won’t have to worry about babies because they can’t change genders, as we clarified in our myth-busting post “Mollies Changing Gender: Is It True?”.

Just don’t try breeding them with fish from another family, such as the Goldfish. We give you the reason why in “Can A Molly And A Goldfish Mate?”. We also answer the controversial issue of breeding with Swordtails in our article “Can A Molly And A Swordtail Breed?”.

Some people keep a single Molly to avoid having them multiply. This is possible, as we point out in our post “Is It OK To Keep One Molly Fish By Herself?”, but technically they live happier lives if they’re kept in groups. And they look great in the tank especially when they shoal.

Some Common Molly Diseases

As we mentioned above, Mollies like to poop a lot. Their high energy dictates a high demand for food, resulting in more waste production.

Thus, most Molly problems stem from unclean water. If not maintained properly, spikes in nitrite and ammonia happen. This is called Molly Disease and features symptoms like shaking and shimmying.

If caught early on, an immediate water change of at least 50 to 70% will reduce the level of toxins significantly and save your fish’s lives. However, prolonged exposure to these toxins may cause several diseases ranging from restlessness to ammonia burns and swim bladder disorder. These are often fatal.

Other diseases may be parasitic, such as ich, velvet, or flukes. These are usually contracted from outside sources, so it’s important to quarantine new fish when they arrive.

Parasitic infections can be treated with Aquarium salt or methylene blue soaks. Raising the temperature also helps relieve symptoms by causing the minute organisms to detach from the fish’s body.

More severe infections can be cured with medicinal treatments, such as Ich-X. If the infection has spread, the whole tank needs to be disinfected.

One deadly Molly disease we’ve mentioned in a previous article is exhaustion after giving birth. It would be best to place these females in a recovery tank for a few days to a week so they can rest and recover.

Fish diseases can be very concerning for any hobbyist. When something is out of the ordinary, you have to find time to observe the fish and test the water right away. Otherwise, devastating consequences may happen. Please read our post “5 Signs Your Molly Is Dying (And What You Can Do)” to see if you can remedy the situation.

Keeping your Mollies’ immune systems healthy will help prevent diseases. If they’re already infected, early diagnosis is key to saving your fish’s life.

Summary

The secret to raising healthy Mollies is first to choose healthy stock. The next thing you need to do is to keep their water clean, give them enough space, feed them a variety of healthy food, and use lots of plants.

If you have questions about Mollies or their care, email us and we’ll do our best to guide you.

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