Why Is My Molly Shaking? (6 Tricks To Treat Shimmies & Vibrates)

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Quite frequently, fish in my tank behave weirdly. For example, several times, I caught my molly fish shaking and vibrating. As the years passed, I learned a few reasons for that issue and understood how to deal with it. Now, I am willing to share my experience.

Molly fish tend to shake due to drops in temperature, usually secondary to malfunctioning heaters or abrupt environmental changes. However, mollies may also vibrate due to inappropriate water conditions, including elevated ammonia, or when the fish is suffering from bacterial or parasitic infections.

As we proceed, I will share a few tricks you can implement in your tank. Those should solve the issue in your aquarium and deal with the shaking molly issue. I will also teach you how to adjust the water parameters properly so that your fish will live longer.

Why Do Mollies Shake?

A shaking molly is what it sounds like, a fish shaking from side to side or merely twitching. Fish can shake for several reasons. For some, it is a mating ritual. They shimmy because they want to attract a mate.[1]

For others, it is a sign of hostility, a means of warning enemies to stay away. Yet, none of those reasons apply to mollies. They are not supposed to shake. But that doesn’t mean they shouldn’t shake at all. 

Fish are unpredictable creatures, and their actions don’t always make sense. A molly that occasionally shakes for short periods shouldn’t concern you. The shaking becomes a problem when it persists. 

That could be related to several causes:

1. The Wrong Temperature

The wrong temperature is just as problematic as the wrong water chemistry. Generally, molly fish thrive in warm waters. If you introduce them to a much colder tank than the ideal temperature, shaking is just one symptom among many that you will observe.

There are two ways in which temperature can cause shimmying:

  • Problematic Heaters – If you don’t have a heater or if the heater stops working, the temperature in the tank will plummet, and the mollies will shake. It is worth mentioning that excessively hot conditions are no better than cold conditions.
  • Prolonged Transportations – Some fish spend so much time in transit that their water temperature falls below the ideal range. That causes distress, but some people make things worse by throwing the fish directly into the tank once it arrives. 

Their objective is to raise the temperature of the fish. However, that drastic shift in temperature can also cause shimmying. You can expect similar results in situations where the new tank’s temperature differs from the store’s temperature where you bought the molly.

Also Read: Molly Fish Temperature

2. Inappropriate Water Chemistry

Molly fish are hailed as hardy fish that can survive in various conditions. However, they are sensitive to soft or acidic water.[2] They may tolerate it for a time, but the Molly fish will start shaking if the water conditions persist. A low pH may burn the molly’s skin.

Also Read: What Is The Best pH Level For Molly Fish?

3. Elevated Toxins

Aquarists should keep an eye on the ammonia and nitrate levels in the tank. Ammonia forms when organic matter rots. That includes fish waste, meal leftovers, and even dead fish and plants.

Ammonia will burn the gills of your mollies, compromising their ability to breathe. It can also kill your molly fish if you fail to reduce its concentration. But before it dies, shimmying is just one symptom among many that will haunt the fish.

Ammonia isn’t the only toxin that aquarists have to watch out for. Detergents are also dangerous. If you fail to rinse the aquarium properly after washing it, the detergent’s residue will poison the mollies.

Some aquarists do not realize that the aerosols they spray in the air can dissolve in the water, making life unnecessarily difficult for their fish.[3] That usually happens in tanks that don’t feature any lid and therefore are not adequately sealed.

4. Your Molly Is Stressed

Stress in molly fish has many sources, including temperature and pH fluctuations, the presence of aggressive fish, elevated ammonia levels, small tank size, and an inadequate diet, to mention but a few.[4]

The easiest way to determine whether or not shimmying in mollies is caused by stress is to look for additional signs. Stressed fish spend a lot of time hiding. They swim erratically and frantically, occasionally crashing into the decorations and walls.

Some mollies will lie at the bottom, while others will gasp at the surface. They may also lose their appetite in the long run. In some situations, their colors will begin to fade. The presence of one or more of these symptoms signifies stress.

Also Read: Stress In Molly Fish

5. Disease

Bacterial and parasitic infections can cause stress in mollies, which, in turn, can lead to shimmying. Some illnesses such as ich create a sense of discomfort that compels mollies to rub against the tank’s objects. Some aquarists may interpret such behavior as shaking.

Also Read: Why Is My Molly Turning Black?

Is This Livebearer Disease?

People used to blame shimmying on livebearer disease, or rather, they called the ailment livebearer disease. Some people still use that term. It is a general descriptor that refers to a situation where hard water or brackish water fish are introduced to freshwater aquariums.[5]

Molly fish that come from stores are not as hardy as those found in the wild. When they are suddenly introduced to a freshwater tank’s conditions, the shock compromises their immune system. 

In some cases, people unknowingly buy stressed fish from the store. The store owner did not bother to acclimatize them properly when he brought them in from the wild. As a result, the new aquarist has to deal with the consequences.

All these conditions and more have been placed under the ‘Livebearer Disease’ category in some circles. You can still use that term if you wish, but it tends to generalize the situation. Ultimately, shaking isn’t a disease.

Instead, it is a symptom that mollies manifest in response to their tank’s poor conditions. If your molly is shaking from side to side, rather than dismissing the symptom as Livebearer Disease, you are better off making an effort to identify one or more of the causes above.

Also Read: 15 Molly Fish Diseases & Their Treatments

How To Treat Shimmies In Molly Fish?

Shimmying is a severe problem. If your molly is twitching, shaking, or seemingly vibrating, it means that the creature cannot control its nerves and muscles. Fortunately, you can help your molly by improving the conditions in its environment. 

Some practical solutions and defenses against shimmying include:

1. Adjust the Water Parameters

It would be best to maintain the ideal parameters in the tank and adjust them to molly fish. That includes a temperature of 72 to 78 degrees F, a pH of 6.7 to 8.5, and hardness ranging from 20 to 30KH.[6]

That is where I highly recommend getting the API Aquarium Test Kit (link to Amazon). That amazing bundle will measure your pH, nitrates, nitrites, and ammonia within five minutes. You can literally perform hundreds of measures within a year, so it is definitely worth the investment.

Also, for mollies, your tank should be at least 10 gallons. It is almost impossible to maintain the right parameters in a tank that is not only small but overcrowded.

The parameters mentioned earlier are more likely to fluctuate in small tanks. And as you know by now, fish require stability in their environment. Don’t forget that soft and acidic water is terrible for mollies. You can use products like Seachem, Calcium Chloride, and Epsom Salt to increase the hardness.

As I mentioned earlier, the tank’s temperature should range from 72 to 78 degrees F. That is the desired range of molly fish. However, within that range, the temperature should remain stable. For example, if today the temperature is 77 degrees F, but tomorrow it drops to 72 degrees F, it is a bad sign.

That is where you should check your heater. The device should be strong enough to keep the temperature stable. If it doesn’t, I highly suggest checking the Cobalt Aquatics Neo-Therm Pro Aquarium Heater (link to Amazon). That is the only device that actually keeps my water stable.

Also Read: Do Molly Fish Need A Heater?

2. Change The Water More Frequently

Water changes are a little tricky. A molly fish that is shaking is already stressed, and a water change can add to that stress, making things far worse. Therefore, it would be best to replace the water as gently as possible.

I suggest performing daily water changes of roughly ten percent. Continue to do these water changes for the next several days. The objective is to improve the conditions in the tank gradually. If you change the molly’s environment too quickly and too drastically, you could make the shimmying even worse.

3. Maintenance

I highly recommend keeping the tank clean. Make sure that you use a filter to keep pollutants out of the water. Also, vacuum the substrate to eliminate fish waste and leftovers. You should also remove any dead organic matter you find.

That will prevent ammonia and nitrate levels from spiking. If the concentration of these toxins rises, use small water changes to bring them under control. Mollies living in a clean tank are less likely to struggle with shimmying.

4. Mitigate Stress

As I mentioned before, stress is a significant cause for shimmies in mollies. If you deal with its causes, your molly fish will likely behave normally and might even live longer. There are several ways to combat stress in a molly fish tank:[7]

  1. Maintain the right conditions in the tank. Avoid unnecessary pH and temperature fluctuations.
  2. Install an efficient filtration system that will keep debris out of the tank.
  3. Install pumps and air stones that can prevent oxygen deficiencies from taking root.
  4. Avoid overcrowding by keeping your fish in a tank of the right size. You should also avoid overstocking.
  5. Make sure the tank has hiding places. Add plants and decorations; the mollies will use them to hide from bullies and any other element in the water they perceive as a threat.
  6. Keep large and aggressive fish out of the tank. That usually includes cichlids such as Angelfish, Discus, and Oscars.
  7. Mollies are schooling fish, and they should be kept in large groups. That will keep the social creatures happy.
  8. Feed the fish on time and in the right amounts. It would help if you didn’t overfeed or underfeed them. Please give them a balanced diet that suits their omnivorous appetites.

5. Consider Salt

Salt baths are quite common in the aquarist community. People use them to bring relief to fish, calming them, and helping them overcome infections. It would be best if you didn’t rely solely on salt baths to cure a sick fish. 

Nevertheless, you are encouraged to place it in quarantine until you identify the disease that causes the shimmying. When you do that, pour one tablespoon of salt for each gallon of water the hospital tank contains.[8] You can use the API Aquarium Salt (link to Amazon), for that matter.

6. Introduce New Mollies Properly

If your mollies spent a long time in transit, avoid throwing them into the aquarium abruptly. They need time to grow accustomed to the warmer conditions in the tank. That is why I suggest placing them in a separate container (a bucket will do).

Add water from the aquarium to the container in small portions (you can use the drip method).[9] Do this for an hour (though, in some cases, thirty minutes are sufficient). Once the fish has acclimated to the tank’s conditions, you can transfer it to the aquarium. 

Another trick is to place the transition bag inside the aquarium. Typically, the bag floats at the top and absorbs the temperature underneath. That will create a gradual equilibrium. After two to three hours you can be sure that the fish has got accustomed.

Also Read: Why Is My Molly Not Moving?


If you found that your molly is shaking, the first step would be measuring the water temperature. If it dropped below 72 degrees F, that is probably the cause. You should also perform regular measures to ensure that the water is stable.

If the temperature is okay, test the water for toxins using a testing kit. You should check for ammonia, nitrites and measure the pH. Each one of those can make your molly shake. Bear in mind that shaking in fish is merely a symptom and not the problem itself.


  1. https://www.tropicalfishsite.com/why-does-my-tropical-fish-shake-its-body/
  2. https://www.ratemyfishtank.com/blog/addressing-the-shimmies-in-live-bearers
  3. https://aquariumscience.org/index.php/11-7-shimmying/
  4. https://www.hartz.com/stress-in-fish-symptoms-and-solutions/
  5. https://www.aquariumcoop.com/blogs/aquarium/livebearer-disease
  6. https://www.fishkeepingworld.com/molly-fish/
  7. https://petcentral.chewy.com/is-your-pet-fish-stressed/
  8. https://www.thesprucepets.com/using-salt-in-a-freshwater-aquarium-1378797
  9. https://petcentral.chewy.com/overcoming-the-shimmies-in-tropical-fish/