Aquarium Molly Fish

Molly fish are some of the coolest aquarium fish on the planet. You don’t need a huge aquarium to keep Mollies either. This site is a resource and community to keeping molly fish. Let’s talk about the most important aspects to keeping mollies.

caring for molly fish

1. Bacteria & Filtration

Make sure you have a descent aquarium filter. Molly fish are pretty messy little fish just because they are constantly eating and moving around so much. The aquarium industry is full of low quality filters! I highly suggest you buy the Aquaclear series filters made by fluval. They have been around for decades and ARE THE BEST hang on the back filter. Here is a link:
The most important factor to your fish aquarium succeeding is having beneficial bacteria. It’s a very complex subject but were going to make it easy for you. Your fish aquarium needs this bacteria to grow OR your fish WILL DIE. When setting up a new tank you can get beneficial bacteria to “jump start” by getting some from an already established tank. Find a friend with a fish aquarium that has been running or go to your pet store and ask for a chunk of their used filter pad to put into your new filter.


 2. Tropical Temperatures

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. Here is a link:
EHEIM Jager Aquarium Thermostat Heater 300W
List Price: $34.99
Price: $31.46
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3. High Quality Food

Feeding molly fish is extremely easy! Feed them a flake food and in the amount of what they eat completely in 5 minutes. The fish foods that “big box stores” sell are terrible quality! If you take a look at the ingredients of these foods.. they will contain what’s known as “fish meal” and that’s bad news! A person needs to spend a couple extra dollars and get a descent quality food. I highly advise buying Omega One Brands. They sell them on amazon and are fairly priced. Here is a link:
Freshwater Flakes 5.3oz.
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4. Good Tank Mates?

molly fish tank
Mollies are rarely aggressive towards other fish. They do great with any of the common tropical fish and south american cichlids. The only problem you might encounter is some mild fin nipping. Just watch your fish and keep an eye on them. Here are some examples of common fish kept with mollies: guppies, platies, angelfish, blood parrot cichlids, firemouth cichlids, gourami fish, black convict cichlids, tetras, and lots more.


5. Water Changer 🙂

Cleaning the gravel is a HUGE deal to keeping your water quality good. If you think about it.. all particles, food, poop and everything falls to the tank bottom. If the bottom of the tank isn’t cleaned it will rot and wreck your water! You also NEED to change out a descent amount of the water once and a while. That’s where we do both at the same time! (read below)


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:


 7. Timer for Lighting

It’s extremely important for fish to have a set schedule for the amount of day versus night. Our fish aquariums need to replicate a natural habitat as much as possible for the fish to be as healthy as possible. A timer enforces for the same time your lights shut off EVERYDAY. This may not seem like a huge deal because “I can remember to turn my lights off”… but it is! Have you ever tried getting a good night rest laying out in the sun???!? That’s my point exactly. These timers cost a couple dollars.. and help so much. Here is a link:
Century 24 Hour Plug-in Mechanical Timer Grounded
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Types of Mollies

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 dalmation 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

Behavior Traits of Mollies

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.

Mollies Breed ALL THE TIME

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.

Water Parameters Needed

The 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.

Common Questions Asked:

molly babies

Use an Air Stone or Bubbler?

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.

What Type of Decorations?

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.

Can I use a 10 Gallon Tank?

It is very common for sources to tell you that you need a 20 gallon tank for these fish, but you can a bit smaller if you have a couple of mollies in the tank. For instance, a 10 gallon tank works for a lot of people and the fish are happy because they have a great home and don’t live in small tiny pet store aquariums. 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 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.

Do I need an Air Pump?

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.

How Many Fish in Tank?

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.