Aquarium Molly Fish Guide


molly fish

Molly fish are some of the coolest aquarium fish on the planet. These fish are known as livebearers (similar to guppies and platies). What makes these fish super cool is they come in so many different color variants. You can have oranges, yellows, black and whites, balloon belly, fancy tailed.. and MORE.

Molly Fish Care & Tank Setup

Different Types and Variants

There are numerous types of molly fish but the most common type held in aquariums is known as the short finned mollies. For the most part, you can categorize them into two different groups of mollies.

Most aquarium mollies are short finned because they are much easier to care for then Sailfin mollies. Sailfin desire a much more wide open tank with more water volume and harder regulated water temperatures. The image shown above to the right is known as a short finned dalmatian molly. Very spectacular in color and shape. The fins on mollies are quite beautiful.

  • Marble Lyretail Molly
  • Harlequin Sailfin Molly
  • Golden Sailfin Molly
  • Gold Dust Molly
  • Gold Doubloon Molly
  • Black Molly
  • Balloon Molly
  • Platinum Lyretail Molly
  • Dalmation Molly
  • Black Lyretail Molly
  • Black Sailfin Molly

molly fish tank

Growth Size & Other Fish

Mollies grow to around 3 inches in length and are rarely aggressive towards other fish. They do great with any of the common tropical fish. It’s important to keep fish of the similar size together. That prohibits from larger fish eating smaller fish. The only problem you might encounter is some mild fin nipping with other tank mates. Just watch your fish and keep an eye on them. Here are some examples of common fish kept with mollies:
  • Guppies
  • Platies
  • Swordtails
  • Tetras
  • Gourami Fish
  • Pleco Catfish

If your having issues with aggression and fighting between fish, you can always add more decorations or plants. Having obstacles in the tank and hiding spots really helps when certain fish are getting picked on. Aquariums with live planted tanks do extra well for these fish.

The old school rule of thumb known as “1 inch” of fish to each gallon of fish is always a safe rule of thumb to play off of. People hate hearing it because some fish are different than others, but it’s just how the rules play out more or less. So if you add those numbers up to your molly fish, they should answer your question. Example, I have one 10 gallon tank and need to know how many Dalmatian mollies I can fit inside.

An average molly fish sees an easy 2 inches of growth, so that puts me at around 4-5 fish in that tank. That is pushing the limits remember too. Just to be safe, I always undershoot this aquarium equation.

What is more important than actual ‘swimming space’ is water quality. This is why pet stores can have very healthy fish in tiny spaces. I always wondered why these resources preached to aquarium owners to have huge tanks but the pet stores can have tiny little tanks with lots of fish… It’s because they are constantly doing water changes from a direct fresh water source. There is no better setup for clean water than to have a direct ‘fresh’ h20 supplement.

molly fish sick

Aquarium Size & Setup

The main reason why we preach that bigger aquariums are better is because they are easier to care for. The fish can pretty easily adapt to the smaller living space but the water quality is the factor that suffers. The more water you have in an enclosed area, the easier it is to be clean. Think of it like making ‘kool-aid’ in the kitchen. The larger container you have of water, the more diluted the mixture is going to be. This is compared to fish poop and uneaten food that sinks to the bottom of your aquarium. The smaller the body of water, the easier it gets dirty.

It is very common for sources to tell you that you need a 20 gallon tank for these fish, but you can use a bit smaller if needed. These fish aren’t going to squeeze into a tiny desk tank like some tetras and guppies do. It is advised that the species of molly fish that get larger in size then 3 inches be kept in a minimum of 30 gallon tanks. It’s just a size thing of them taking up so much room in the actual aquarium.

The issue of an aquarium having too much oxygen is never a bad problem to have. If your fish don’t have enough oxygen.. they are going to die very fast. Mollies and other livebearing fish do not mind the air bubbles in their tank and bubbler setups can really add value to your tank other than oxygen. If your thinking of setting up an air pump setup, maybe look into small sponge filter setups because they run from bubbler setups and really can filter your aquarium water very good while you also getting the added benefit of an air stone. You can really get two sides of benefit with one device on this one. The sponge filter setup is a very under-rated aquarium filtration method. A lot of breeders even today use sponge filters over all the leading technology in aquarium filtration. It’s simple and hard to beat.

molly fish tank

Water Temperature & Heaters

Mollies are tropical fish so that means you need an aquarium heater. The water temperature should be between 78 to 82 degrees Fahrenheit. When you buy a heater figure on needing 5 watts per 1 gallon of water in which your aquarium size is. Buying a quality brand heater usually means they are more safe (don’t explode) and save on your electricity bill. These new Eheim Jager heaters have been taking over the market lately because of their low cost and quality components.
If you have a filter running on your tank you don’t necessarily need an air pump but it’s a good backup in case your filter fails. We always advise people to buy an air pump and throw on a sponge filter instead of an air stone. They do the same thing except they filter your water TOO! It’s knocking out two birds with one stone “sort of say”.. And again, if your filter fails that sponge filter will probably save the tank by itself.

molly-shaking-head

Best Foods & Schedule

Feeding molly fish is extremely easy! Feed them a flake food and in the amount of what they eat completely in 5 minutes. Some argue that these fish prefer only algae and plants, but I find they are very opportunistic. It’s important to buy a brand of food that isn’t low quality. Some of them are absolutely terrible and the fish hate them. A person needs to spend a couple extra dollars and get a descent quality food. I highly advise buying Omega One Brands.

Tank Maintenance and Cleaning

A water changer is a device that will change your LIFE. It hooks up to your faucet (bathroom, kitchen, etc). It has a switch on it that makes so water is pushed through the hose and also pulls water into the hose. It sounds confusing.. but it’s not. All you do is hook it up to your faucet and then pull water out of your aquarium (while sucking/cleaning the gravel) and then when done.. hit the switch.. and then fill aquarium back up with new water. Just trust me on this.. YOU NEED ONE. Here is the link:

Molly fish are considered to be “mid level” swimmers and really love all decorations. I’m not going to tell you that some decorations are better than others because it’s not completely true. The only factor to keep into consideration is the fact of your fish being able to hide from bullies. In all aquarium circumstances there is going to be more aggressive fish along with more timid of fish. The timid fish will get pushed around and chased. It’s important to have enough hiding spaces for those scarred fish to hide and feel safe in certain scenarios. The more plants your tank has, the safer it is going to be for aggression levels becoming dangerous.

Aggression With Other Fish

These guys are known to nip at other fish’s fins but it’s not to a drastic measure. They are for the most part very peaceful and to themselves. What I find very unique about Molly fish is the fact that they setup a division of hierarchy. Each Molly fish is going to have his or her level of importance and they live and die by these levels. I think of them as little soldiers that have different role ranks. People thought I was crazy for saying this until they actually realized it was happening right under their eyes.

I’m not quite sure why they do this hierarchy of levels but it’s just how the fish is. You will see a fish with less rank come up to a fish that has more power and it’s almost as if the fish is kissing his shoes “sort of say.” They will back out of each others way and do lots of unique things regarding their rank levels. I have had 0 incidents as far as the fish being over aggressive with other tank mates in the same habitat level. Very peaceful and civil to be around for other fish in the same habitat of living.

Quick Fact: Male Mollies are the Alpha Fish
You will quickly find out that the males are the king and most alpha when it comes to rank of the molly fish. They are the most beautiful as well. One male with three females is going to give your tank a very safe environment. This gives the male a chance to choose one out of a pack instead of forcing his way into what has to be done. Having numerous males in one tank will cause lots of aggression with Alphas fighting.

Pregnancy, Breeder Boxes, & Babies

After owning molly fish or any livebearer for some time, you will quickly find out how much they breed. Any molly fish can breed with another breed of molly. This makes for a crazy successful breeding platform. Any female can hookup with any male. Being livebearers, they do give ‘live birth’ to their babies. Females are usually always pregnant with babies and that’s how you can cosmetically tell the difference between males and females. That and fin differences.

The parents will feed on their newly born young and that makes for a nice snack. It’s pretty disturbing but you get over it. If they didn’t eat their own young.. there would be molly fish everywhere I think… It’s not uncommon to see 1-3 babies swimming in your tank that somehow survived the birth and feeding of the newborns while you were at work all day.

Type of Water for Mollies?

molly fish wont eat bottom tankThe recommended temperature range for Mollies is 75-80° F since it is native to tropical parts of the world. The pH should be between 7 and 8, and using driftwood in the aquarium is therefore not recommended since driftwood is known to lower the pH value. Mollies will do best in a decorated aquarium where a big open area has been left from swimming around in.

Molly fish are said to be brackish water fish (freshwater mixed with saltwater) but the rate of saltwater should be very weak. Most molly fish that we buy as fishkeepers from pet stores are going to be most used to regular freshwater and that’s what you should go with mostly. Salt in your freshwater does help out with bacteria and such but if you have other freshwater roommates.. it makes it hard to put salt in the water and mix up their water parameters juts to make the mollies a little happy. They will do just fine with plain freshwater and you can add small amounts but I personally wouldn’t get too buck wild with adding salt.

 

Please help me.

All my fishes are dying. I can’t identify what kinda disease is this. I can see some tiny hair like things on their body. I’m growing Guppies, mollies, wrestling half beaks and a betta in my community tank. All the fishes including my betta also got affected with it. All of a sudden my Guppies dies the next day since I encounter those hair like things. I’ve lost my favorite breeds one by one every day. These fish’s organs and body systems work well in the wild. Ended up with 3 alive from 10 fishes. Also my mollies and betta too affected from that unknown thing. They are getting leaner and leaner day by day. For the past two days, no fish is taking food. I’ve tried to pluck them from the body, and failed. My new fries too died within a day with those hair like shit present on their body. When my Guppies are affected and almost crossed the level of survival, their tails and body colour gets faded. Tails got tore. I can’t find any solution on Internet or YouTube. Please help me to make at least a few fishes to survive.

I dont know how you weren’t able to find information on anchor worms… I found pages upon pages of information. Also, several videos on Youtube… There’s tonnes of info out there, if you do a tiny bit of research.
I can’t get what kinda thing was that. So I was unable to get any info about anchor worms. But later I gone through several videos and now operating my fishes and plucking those shits from them and waiting for a couple of bottles of paracidol for further medication.
Your tank might be infected, remove your fish from the tank and examine it one by one remove it by tweezers and place it on quarantine tank that has 1 teaspoon of salt per gallon. Since  i dont have  heater or med i expose them from the sun and daily 30% waterchange. Do a 100% water change on ur main tank. Anchor worm will die eventually if they dont have fish to attach with. Let it rest for 3 weeks it depends what is the temp of ur water. The higher the temp the fastest it will develop to mature. Let us also wait for other who uses med for cure.
Heating up the water could definitely help as well as cleaning. I use to have alot of issues with parasites in the tank years ago and would buy the drops and medications and they did work, but eventually I figured out cleaning and heating the tank for a couple of days actually worked and it’s been parasites free for 3 years. I also do a 30-50 percent water change every Saturday and that seems to help alot.
Hi guys,

I joined to ask a question about my multi colored molly. Does it look like a female and pregnant? It used to swim around the cage happy now it jus sits up in the corner away from the other fish.

The pure white one seems to chase the multicolored one and the pure black one constantly. Is this because the white one is a male ?

Does anyone know how diverse the genetics of store bought mollies are?  Right now my few fish are bought at three different times from two different stores (and they are all slightly different, black, silver, creamsicle, gold dust etc.).  In order to try and keep from having all my fry having the same genetics and breeding together and inbreeding further, is there value in me buying from another store in another town, or are mollies generally all from one farm and inbred already? swollen stomach molly fish
I’ve thought about this, too. You could attempt to find out who they get their fish from — which distributor they use. And then attempt to find out which farm the distributors source from.

And then go collecting in Texas or Florida to diversify the genetics.

even if I had a pair, they don’t selectively breed with only their mate.  The males are sleeping around.  I just want healthy fish, not necessarily purebred, my understanding of most the mollies we get are they are all hybrids anyhow.
Ok, So I recently started keeping mollies again, but I bought 3 girls and a male, and my black female gave birth to 20 fry the day after I got her, then just 20 days later gave birth to another 20, so I now have 40 tiny babies and both other females are pregnant too… I’m running out of space!!
I’m having the same thing happen! Lol I ended up just selling my only male! *he was a busy one!* I only have a 40 gallon tank with about 50 Molly’s in it..so I do extra water changes for now until they get big enough and I’m going to sell the males. I’m apart of a local fish group and everyone is awesome and took a lot of these guys off my hands! I suggest putting live plants in there if you haven’t already to keep the perimeters in range.. Good luck!! They are breeder machines!
I have the babies in a separate floating mini tank within the 15 gallon tank but they are still too small to move. How long did it take yours to get big enough for the community tank?
It might sound cruel, but in my tank I’ve made a point of not separating the fry so many get eaten.  I have never seen the 20 fry happen that I read about.  I imagine they are taken care of too quickly, I likely miss full batches of fry even.  Right now I have 5 females and 1 male, 5 fry, one that is getting pretty big, not really fry anymore.  So the short answer for me is I let nature be the population control.
I would call local pet stores and see if they would be willing to take some of your extras. My local store even gives me credit to purchase supplies which is nice.
Got cleared that my fishes got affected with anchor worms. Operating all my fishes and plucking those shits from them and waiting for a couple of days to get paracidol med which could arrive by Thursday. As of now, using heater, filter, rock salt and almond leaf extract to my tank. Will be happy if my fishes survive till Thursday since I will start medication immediately after the arrival of med.
Ok all I need some help. I have a female black Molly that seems to get Ich anytime she isn’t in isolation. She normally lives in my 75 Gallon community tank. Problem is after a few days she gets white spots and so I move her to my 10 gallon hospital tank treat her and once she is healed I leave her a few days on to make sure she is good then move her back and sure enough a few days later she gets ich again. She is the only fish that gets it. None of the other Mollies do… Any ideas?
I personally won’t get any more Mollies right now until I can have a salted tank. In my opinion, mine have suffered health issues from not living in a salt environment. I lost them all over time. This breaks my heart because Mollies are my favorite.
I had some collected native green mollies in an outdoor stock tank, moved a couple in  to my 38. They were in poor shape and had recurring ich, they would recover and look normal for a week or two and then get it again and go down hill.  The male finally developed a kink in his back and died.  The female has been fine for a month, so maybe the cycle has broken.  No other fish in the tanks got it.  I was reluctant to add a lot of salt because of the plants.  I have put a cuttlebone in the tank to add calcium, which my help.
I am going to be silly enough to attempt a few muppies or gollies. I have a golden dumbo fin guppy and I see a gold molly online I gotta try I know it won’t be able to breed and survival rate is poor but if I can get even one golden muppy I’ll acclimate it to salt and keep it in my sump.
I ordered the guppies on Ebay from Thailand, after I paid the guy I find out you have to have a exotic pet license to import them. 3 of 8 doa to a transshipper who held them hostage for 3 weeks after taking the money from me no communication they got here valentine’s day.. Any one importing fish should use someone other than Linda Osen from Colorado it was a nightmarish experience