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Can Mollies Live With Goldfish? (5 Tips for Coexistence)

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Both mollies and goldfish are prevalent in the fishkeeping world. For that reason, more than once, I’ve been asking myself whether they can live together in the same tank. As I tried different combinations over the years, I learned a few insights on mollies and goldfish. Now, I am willing to share my experience.

Mollies and goldfish can live together in the same tank, although it is not recommended. While mollies require warm temperatures, goldfish thrive in cold water that may stress mollies. Also, mollies are hard to predict and can become aggressive towards goldfish, particularly during mealtimes.

As we move forward, I will show you what steps you should take if you still wish to grow mollies and goldfish in the same tank. I will also list the best tankmates for both mollies and goldfish, so you can easily find alternatives.

Mollies and Goldfish: Will They Get Along?

A tank with both goldfish and mollies would be delightful because they are both colorful and easy to grow. However, many aquarists are convinced that these two species cannot coexist. Yet, that shouldn’t necessarily stop you from trying to keep them in the same tank.

There are ways to compensate for the factors that make mollies and goldfish so different from one another. However, they are not the best match for each other. You can tell by looking at their attributes:

1. Goldfish are Bigger than Mollies

The size matters because fish eat whatever they can fit in their mouths. This is especially true for goldfish. They are fast swimmers that have been known to swallow smaller creatures in the tank unintentionally.[1]

At an average of 6 inches, goldfish are a danger to fish that are drastically smaller than them. But at 4.5 inches, mollies are a decent match for goldfish. They are also fast enough to stay out of reach of your goldfish. 

For that reason, where these two fish are concerned, the size isn’t a significant factor. However, you should take size differences into account when the mollies are relatively young. In that case, they will be easy prey to the robust goldfish.

2. Mollies Require Warmer Temperatures

The water requirements are an issue. Goldfish are not that particular where the pH is concerned, though you should keep it between 7.0 and 8.4.[2] Molly fish are no different in that regard. They require slightly alkaline water ranging between 6.7 and 8.5.

But that isn’t the case with temperature, which is your most significant complication. Goldfish thrive in relatively cold water. They are happiest in tanks with a temperature of 68 to 74 degrees F. Mollies, on the other hand, need warmer conditions ranging between 70 and 82 degrees F.

Keeping both species in the same tank means forcing one of the fish to adapt to temperatures they do not necessarily enjoy. While this can be done, it isn’t ideal, at least not for fish. But of the two, mollies are seemingly less sensitive where the temperature is concerned.

3. Mollies are Hard to Predict

Both species are peaceful and friendly. They are also exceptionally social, which means that, in an ideal situation, they will welcome one another’s company. However, mollies are unpredictable. In the right circumstances, they can manifest aggressive behavior.

Once this happens, they can become notorious fin nippers that may eat the slime off your goldfish’s body, making life for the creature quite tricky. If you have slower, more docile types such as fancy goldfish, aggressive mollies will bully them.

4. Mollies can be Aggressive with Food

Neither species is particularly challenging where their feeding habits are concerned. They are both omnivores, which means that they can eat the same meals.[3] For example, both mollies and goldfish eat a lot of plants and algae in the wild.

It would help if you replicated this diet in the tank by adding sufficient amounts of vegetables to their meals. But for the most part, neither species will make mealtimes difficult. Nevertheless, as was mentioned above, some mollies are aggressive.

That means that slower goldfish cannot compete for food with hostile mollies. This is one of the reasons that discourage some aquarists from pairing the two species. The unpredictability associated with mollies makes them a gamble. On the other hand, you could just as easily land a peaceful molly.

5. Goldfish are too Messy for Mollies

Hygiene is another important consideration. Molly fish are hardy and can survive in tanks whose pH and temperature are not ideal. That being said, they are quite sensitive where hygiene is concerned. They need a clean, well-maintained tank.

This is a problem because goldfish are messy and produce a lot of waste.[4] For that reason, if you wish to grow goldfish, I suggest that you get a robust filtration system. That will prevent the tank from deteriorating. 

Also, placing goldfish in warm conditions such as those that a molly prefers will enhance their metabolism. They will eat more food, producing a lot more waste in the process. In other words, they will make it that much harder to keep the tank clean.

How to Make Mollies and Goldfish Live Together?

It isn’t the best idea to keep mollies and goldfish in the same tank. That being said, numerous aquarists have successfully reared both species in the same aquarium. While keeping them together is difficult, it isn’t impossible, not if you keep the following in mind:

1. Adjusting the Temperature

As was mentioned, temperature is your biggest obstacle. Neither species is that picky where the pH is concerned. However, mollies like warm water, whereas goldfish thrive in colder conditions. 

You cannot appease both creatures, so your only option is to maintain a cold tank (68 to 74 degrees F). As was noted above, warm water increases a goldfish’s metabolism, which, in turn, encourages the creatures to make more of a mess. 

Additionally, of the two species, mollies are less sensitive to the temperature. They can survive in cooler conditions. But the water shouldn’t be too cold. Find a temperature that falls somewhere between the preferred conditions of both fish.

It is also crucial to keep the temperature stable. Since your mollies won’t get their ideal conditions, you should prevent fluctuations by all means. That is where I highly recommend checking the Cobalt Aquatics Flat Neo-Therm Heater link to Amazon).

After trying numerous heaters, I can say that the Cobalt is the best choice. While it is a bit above average, it will prevent you from getting low-quality heaters that will eventually be thrown away. That will save you money down the line. If you’d like, I also reviewed the device here.

2. Ensuring Hygiene Conditions

You can’t do anything about the goldfish’s penchant for making a mess. Your only option is to install a powerful filter and to carry out more frequent water changes. I personally use the MarineLand Penguin 100 Power Filter (link to Amazon), which works flawlessly in my 20-gallon tank.

But before you place these two fish in the same tank, you should take a moment to determine whether you are willing to do the extra work. Otherwise, if your cleaning protocols cannot keep up with the goldfish’s messy nature, the tank’s conditions will become toxic to the molly fish.

3. Getting the Right Tank Size

Bear in mind that both fish require tanks of at least 20 gallons. A small tank is more likely to encourage bullying. I suggest that you give your mollies and goldfish the space they need to explore without repeatedly running into one another.

An aggressive molly is less likely to harass its goldfish neighbors in a spacious tank. On the other hand, a cramped tank will produce the opposite results. If your current tank is too small, feel free to check my recommendations for aquarium kits.

4. Adding Plants and Decorations

Both species prefer planted tanks to their bare counterparts. Plants and decorations will maintain the peace in the aquarium by alleviating stress in your fish. If your mollies misbehave, the goldfish can also use the plants to hide.

5. Picking the Right Numbers

Molly fish are social creatures. For that reason, you should keep them in groups of four or more. The presence of other mollies will make them happier and less fearful. This, in turn, will make them less likely to harass their tankmates.

However, you shouldn’t have so many fish that your aquarium becomes overcrowded. An overcrowded aquarium encourages violence and bullying. You should also take vegetation into account. Position your plants in a way your fish can freely swim.

What Kinds of Fish Can Live with Mollies?

The kinds of fish that can live with mollies typically feature similar size and temperament to molly fish. That usually includes species like Guppies, Platys, Tetras, Swordtails, and Endlers. Besides similar characteristics, those fish also thrive at the same temperature and pH as mollies.

If you have no experience with those species, here is what you should know:[5]

  • Guppies – Guppies are small, colorful fish. They have a friendly attitude that makes them compatible with other friendly fish. Because they are fast swimmers, they can steer clear of any aggressive fish in the tank.
  • Platy Fish – This is another small and fast species. Like guppies, platys are quite friendly and get along with their neighbors. New aquarists will appreciate them because they are so easy to care for. Also, they don’t take up that much space.
  • Tetras – Tetras come in various colors. They are social fish that should be kept in large groups. This tells you that they do not mind the company of friendly species like mollies. As omnivores, they can eat the same meals as your mollies.
  • Swordtails – Swordtails are also suitable for beginners. Available in a decent array of colors, they are quite hardy, capable of surviving in various conditions. Their peaceful behavior makes them great companions for mollies.
  • Endlers – Endlers are similar to guppies in many ways. Their small size makes them unsuitable companions for large, aggressive fish. But they can survive in a tank with mollies if the conditions are appropriate.

What Kinds of Fish Can Live with Goldfish?

Goldfish are likely to happily live with Rosy Barbs, Loaches, Zebra Danios, Plecos, and Corydoras. These species are relatively peaceful and match the size of the goldfish. Those fish also require similar conditions as goldfish, including pH, temperature, filtration, and tank size.

If you have no previous experience with those fish, here is what you should know:[6]

  • Rosy Barbs – Rosy barbs are considered attractive tankmates because they are social and enjoy the company of other fish. Like goldfish, rosy barbs grow to an average of 6 inches, which means that goldfish cannot eat them. They also don’t require that much attention.
  • Hillstream Loach – The Hillstream Loach likes cold conditions, just like the goldfish. It is an attractive tankmate for goldfish because it is a scavenger that will eat food scraps and algae. In other words, it is unlikely to fight with your goldfish over food. You can also pair the goldfish with other loaches, such as the Chinese butterfly and Borneo sucker loach.
  • Zebra Danios – Zebra danios thrive in the same cold temperatures as goldfish. They are small enough for goldfish to eat. However, they are also fast enough to escape hungry goldfish if the need ever arises.
  • Bristlenose Pleco – Plecos are tricky because they have a reputation for sucking on the slime coat of species like goldfish. However, this is less likely to happen with a Bristlenose Pleco, especially if you keep it well-fed.
  • Banded Corydoras – This is a social fish that is happiest in large groups. It is also peaceful. At four inches, you don’t have to worry about your goldfish eating the creature. It can live in the same cold temperatures that goldfish prefer.

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Conclusions

Keeping both mollies and goldfish in the same tank may pose a challenge. That is because goldfish prefer cold water, while mollies require slightly warmer conditions. Also, mollies are messy and unpredictable, two qualities that are not suitable for goldfish.

If you still wish to keep goldfish with mollies, it is better to adjust the goldfish’s temperature (68 to 74 degrees F). Also, make sure that the tank is large enough (at least 20 gallons) and features sufficient vegetation and hiding places.

References

  1. https://www.aquariumcoop.com/blogs/aquarium/goldfish-tank-mates
  2. https://www.aqueon.com/information/care-sheets/goldfish
  3. https://www.thesprucepets.com/the-mollie-1380726
  4. https://guppyexpert.com/guppies-goldfish/
  5. https://www.buildyouraquarium.com/molly-fish-tank-mates/
  6. https://modestfish.com/goldfish-tank-mates/#content