Can Mollies Live In Cold Water? (Without A Heater)

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The longer I grew my molly fish, the more I got interested in their survival capabilities. I intended to add them to my goldfish’s tank, which didn’t even feature a heater. To make sure my mollies won’t die, I began researching whether they can survive and live decently in cold water.

Mollies can live in cold water without a heater, possibly even in ponds. However, they will probably fail to thrive under those conditions. Temperatures below 78 degrees F will make them vulnerable to diseases, stunt their growth, and prevent pregnant mollies from giving birth.

As we move forward in this article, I will share a few signs indicating that your molly is suffering from an inappropriate temperature. I will also discuss whether you may keep your molly fish in a pond, and how you should do so.

Also Read: 15 Things You Should Know About Molly Fish

Can Mollies Survive in Cold Water?

Some fish thrive in cold water. One example is goldfish.[1] They prefer colder environments, and they live longer than their tropical counterparts. Mollies are not coldwater fish. But that won’t stop people from putting them in cold water. This is what you have to understand about such situations:

Yes, mollies can live in cold water. As most professional aquarists will tell you, mollies are hardy fish. They can survive in temperatures that are either slightly higher or slightly lower than the ideal. While colder temperatures are detrimental to them, don’t expect them to roll over and die. 

They might not thrive, but you can probably trust them to live with these conditions for a while. In truth, drastic temperature changes are more dangerous to mollies. Wild swings between heat and cold will harm them, so any changes have to be gradual. Once you realize that your fish need warmer waters, you can’t just raise the temperature at once.

1. Should Mollies Live in Cold Water?

No, they shouldn’t. Yes, mollies are robust and hardy fish that can survive in cold water. However, the wrong temperature will have adverse consequences for their health. It will impair their immunity, leaving them vulnerable to shimmy, ich, and various other illnesses.

There is a big difference between surviving and thriving. Mollies can survive in cold water. But they need warmer waters to thrive. The ideal temperature will produce healthier mollies while also encouraging optimal breeding. 

The fry your adult mollies produce will grow faster, and they will remain free of deformities. They will develop more attractive features and more vibrant colors. This is true for any fish that is allowed to live in a tank with the right parameters.

2. Can Mollies Live Without a Heater?

Yes, mollies can live without a heater. It was already noted above that they are hardy and robust fish. It was also noted that they could survive poor conditions, although that doesn’t necessarily mean they will thrive in those. 

In other words, it isn’t a question of whether or not they can live without a heater but, instead, whether or not they can thrive without a heater. The answer to that question depends on various factors, with the most prominent being the weather.

People that live in regions with tropical climates can maintain tanks without heaters, especially if their temperatures never fall below 68 degrees F.[2] In tropical regions, you can trust the ambient temperature to warm the water in the tank.

Of course, this doesn’t account for unexpected changes in the weather. This is why heaters are preferable. Their presence allows you to maintain a consistent temperature in the tank regardless of the conditions outside the tank.

People that don’t use heaters are slaves to the weather. The conditions in their molly tanks will continue to change in response to weather conditions until they install heaters. And as was observed before, mollies don’t appreciate sudden changes in temperature.

But if your weather is warm and stable, then it is possible to maintain a healthy molly tank without a heater. Aquarists who are not fortunate enough to live in tropical regions often rely on heating systems to keep their tanks within the appropriate range. 

On the other hand, you can tell that the water is too hot for your mollies if they spend too much time at the bottom.

But air conditioning units are not reliable solutions to your molly tank’s heating problems. When it comes to indoor aquariums, because water temperature rises and falls at a slower rate than the air temperature, the temperature of your tank won’t necessarily match the temperature of your home.

In other words, raising the temperature in your home won’t necessarily elevate the tank’s temperature. If various circumstances have prevented you from securing a heater, you can use your home’s heating mechanisms to maintain your tank.

But you are still encouraged to purchase a heater the first chance you get. This is the only way to maintain the temperature at a healthy level. The word ‘maintain’ is crucial. You have to keep the temperature consistent. You cannot rely on your region’s tropical climate or your home’s heating system.

Also Read: Do Molly Fish Need A Heater?

3. What Temperatures Can Mollie Live in?

Mollies prefer warmer water. They thrive in temperatures ranging from 78 to 82 degrees F.[3] As was mentioned earlier, you can achieve that range without using a heating device. Yet, even if the temperature falls within that precise range, fluctuations may cause problems.

For example, if the water temperature is 79 degrees F on one day and 80 degrees on the following one, that isn’t ideal. Your mollies will have to continually readapt, which may deteriorate their health and force them to change swimming positions frequently.

Also Read: Molly Fish Temperature

Can Mollies Live in a Pond?

A lot of aquarists keep their fish indoors. But you don’t have to if you don’t want to: 

  • While fish in tanks are fun to observe, fish in ponds and fountains are even more spectacular because they have so much more room to maneuver. The presence of fish can also have a transformative effect on your yard.
  • Fish can fend for themselves in ponds. There are plenty of insects and larvae on the outside that they can eat to satisfy their cravings. You don’t have to worry as much about their feeding habits.

That being said, not everyone can afford to keep mollies in ponds, since the weather is crucial. You need tropical weather to rear fish outside. If the temperatures in your region keep falling below 68 degrees F, you are better off growing your mollies inside.

Then again, nothing is stopping you from doing both. That is to say; you can keep your fish in a pond in the summer when the weather is appropriate. But once winter comes, you can simply move the mollies back indoors. If you don’t have a pond, they can also survive in a tub.

Ultimately, the temperature is your primary concern. Mollies can live in ponds in the summer because the sun can keep their water sufficiently warm. You can’t keep them outside in the winter because the temperature will drop to dangerous levels, eventually killing them.

But what about nighttime? If they rely on the sun’s rays to warm their water, do you have to bring them inside at night to protect them from the drop in temperature? No, you don’t. The absence of the sun at night will cause the temperature in the air to fall. However, the decrease in temperature in the pond won’t be that significant. Your mollies can survive until the sun rises in the morning.

What about brutally warm summers? Can your mollies survive in a pond on excessively warm days? Well, mollies are as sensitive to hot water as they are to cold water, and it is more than possible for the sun to overheat the water in the pond.

One option is to keep your fish inside during dangerously hot seasons. But rather than frequently moving your mollies back and forth between the pond and their indoor tank, you are better off creating shade around the pond that will prevent intense sunlight from overheating the water.

Ponds are somewhat problematic, especially the kind found in most people’s homes. They are small, restrictive water bodies. In the wild, when the temperature changes, mollies will leave in search of regions whose water temperature is more favorable.

But they cannot do that in a small backyard pond. They have to make do with the available temperature, which is why you have to control the temperature on their behalf. One way of protecting your mollies from the wrong temperature is to ensure that their pond is partially submerged in the earth. 

This will allow the water to remain within the appropriate temperature range. If you’ve chosen to construct a fountain, it should have substantially thick walls to achieve a similar effect. You don’t want the water to be in direct contact with the tropical environment.

While mollies in ponds can fend for themselves to an extent, you are still encouraged to provide them with a planted environment. Like an indoor molly tank, the pond in your backyard should mimic their habitats’ properties in the wild.

Mollies like aquatic plants. First of all, they can nibble on them if the need arises. Secondly, plants provide shade. Your mollies can use them to escape intense sunlight. Third, plants provide protection. Your mollies can use them to maintain their privacy or to hide from other fish in the pond.

Also Read: 11 Plants Your Molly Fish Will Love In Their Tank

Speaking of hiding, if your pond has a variety of fish, keep your molly fish’s safety in mind. Mollies are peaceful fish that cannot live with more substantial, aggressive species like cichlids.[4] But other fish are not your only problem.

Ponds expose mollies to deadly predators like cats and birds. This is why plants are so important. Mollies can use them to hide. If you don’t trust the plants to keep your mollies safe, introduce caves at the bottom. You should also consider removing dangerous fish like convict cichlids.

Don’t forget to acclimate your mollies to the pond before you make the transfer. Place your fish in a bucket filled with both pond water and tank water.[5] Give the mollies a chance to grow accustomed to the pond water. Before you make the transfer, place the mollies in a plastic bag. Then, float the bag in the pond for a quarter of an hour. Once the temperature equalizes, you can release the fish.

Also Read: Do Molly Fish Sleep?


Mollies can live in cold water. They will probably do just fine in tropical environments that do not get too cold. However, if your area gets too cold during the winter, the ambient temperature may pose an issue to your mollies.

Ideally, molly fish thrive in temperatures that range between 78 to 82 degrees F. If the temperature gets lower than that, you probably need a heater. You should also keep in mind that temperature fluctuations aren’t healthy for your fish. That is another factor that a heating system eliminates.

When it comes to a pond, the considerations are about the same. However, you shouldn’t worry too much about the drop in temperatures during nighttime. Ponds are pretty resilient to short term changes. The winter period should worry you more, and if the cold is unbearable, consider moving your mollies indoors.