Why Is My Molly Fish Breathing Fast? (With 5 Solutions)

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I know how worrying it can be to see your molly fish breathing rapidly. When I saw that a few years ago, I was sure that I was about to lose my fish.

However, as I gained more experience in this field, I learned that this is a pretty common symptom that can be treated effectively by following the right steps.

In this article, you will learn what causes labored breathing in molly fish, how to treat it, and how to prevent it from happening again in the future.

Let’s get started.

Why Is My Molly Fish Breathing Rapidly?

Several factors might have caused your molly fish to breathe fast. Here are the most common ones:

1. Insufficient Oxygen Levels

Oxygen is a critical component for the survival and well-being of your molly fish. If oxygen levels are insufficient, molly fish may resort to rapid breathing to meet their metabolic needs. 

Consider the following points:

  • Insufficient Surface Movement: Without adequate water surface agitation, oxygenation reduces, leading to molly fish breathing rapidly to compensate.
  • Overcrowding: An overly populated tank quickly depletes oxygen levels, causing molly fish to breathe faster.
  • Poor Filtration System: An ineffective aquarium filter fails to oxygenate the water properly, leading to molly fish distress.
  • Plants at Night: Aquatic plants absorb oxygen during the night, which can lead to insufficient oxygen for molly fish.
  • Poor Maintenance: Low oxygen levels can arise from a poorly maintained aquarium, causing molly fish to breathe rapidly.

2. Stress

Molly fish are sensitive creatures, and stressful conditions can easily affect them. This stress can manifest in physical symptoms such as rapid breathing.

Here is what you should know:

  • Poor Handling: Frequent or rough handling stresses molly fish, causing them to breathe faster.
  • Rapid Changes: Sudden changes in water temperature, pH, or other parameters can lead to stress and rapid breathing in molly fish.
  • Aggression: Housing molly fish with aggressive tank mates can lead to stress, and subsequently, rapid breathing.
  • Inappropriate Environment: A lack of adequate hiding places and swimming space can stress molly fish, causing faster breathing.
  • Poor Diet: Feeding molly fish an improper diet can cause stress, leading to symptoms like rapid breathing.

Also Read: Stress In Molly Fish

3. High Water Temperature

Molly fish thrive in specific temperature ranges, and a deviation can cause them to exhibit signs of stress, such as rapid breathing.

Keep the following in mind:

  • Temperature Beyond Range: If the temperature exceeds the comfortable range of 70-82°F (21-28°C) for molly fish, they may breathe rapidly.
  • Rapid Fluctuations: Sudden increases in water temperature can stress molly fish, leading to rapid breathing.
  • Inadequate Cooling: A lack of proper cooling mechanisms during hot weather can cause rapid breathing in molly fish.
  • Overheated Equipment: Equipment like lighting that overheats can increase water temperature and lead to rapid breathing in molly fish.
  • Insufficient Aeration: High temperatures reduce the water’s capacity to hold oxygen, leading to rapid breathing in molly fish.

Also Read: Molly Fish Staying At The Top Of The Tank

4. High Ammonia Levels

Molly fish are notably vulnerable to the quality of their water environment, and elevated ammonia levels can turn deadly.

The signs of this harm include quicker-than-normal breathing. Here are some essential points to keep in mind:

  • Overfeeding: If molly fish are given excessive food, it results in surplus waste that can spike ammonia levels, causing fast breathing.
  • Dead Organisms: When plants or animals in the tank decay, they can up the ammonia levels, which can induce rapid breathing in molly fish.
  • Poor Filtration: An ineffective filter can’t efficiently eliminate ammonia, leading to discomfort and quick breathing in molly fish.
  • Rare Water Changes: If water changes aren’t frequent, ammonia can gather in high amounts, which can cause swift breathing.
  • Uncycled Tank: If the tank isn’t properly prepared, or “cycled,” before bringing in molly fish, ammonia levels could surge quickly, leading to fast breathing.

5. Disease

Sickness or diseases can strain molly fish, resulting in physical signs like increased breathing. Here are some important factors to consider:

  • Infectious Diseases: Illnesses such as ich or fin rot can put molly fish under stress, triggering increased breathing.
  • Parasites: Parasitic infections can cause discomfort and stress, resulting in rapid breathing in molly fish.
  • Bacterial Infections: Bacterial diseases can stress molly fish and lead to rapid breathing.
  • Poor Water Quality: Poor water quality can lead to various health issues, often causing molly fish to breathe rapidly.
  • Poor Nutrition: An improper diet can lead to weakened immunity, making molly fish more susceptible to illnesses that cause rapid breathing.

Also Read: Why Is My Molly Fish Blowing Bubbles?

How to Treat Molly Fish Experiencing Rapid Breathing

Fortunately, there are some basic steps you can take to treat your molly fish. Here is what you can do:

1. Managing Oxygen Deficiency

To alleviate your molly fish’s distress, it’s crucial to ensure the tank has adequate oxygen. Addressing an oxygen deficiency can help normalize their breathing rate.

Here are some practical steps:

  • Improve Surface Movement: Install devices like air stones or water pumps to enhance surface agitation. Aim for visible but gentle waves on the water surface. My recommendation: Hygger Aquarium Air Stone (link to Amazon).
  • Control Population: As a general rule, provide at least 1 gallon of water for every inch of fish to prevent overcrowding and maintain suitable oxygen levels.
  • Upgrade Filtration System: Invest in a high-quality aquarium filter, such as a canister or sponge filter, which can improve water oxygenation by up to 70%. My recommendation: Fluval C4 Power Filter (link to Amazon).
  • Manage Plant Presence: At night, turn on an air pump or other oxygen source to counter plant oxygen absorption and maintain an oxygen level above 5-7 mg/l.
  • Regular Maintenance: Perform regular cleanings every 2 weeks and replace 25% of tank water to keep oxygen levels optimal.

Also Read: Do Molly Fish Need A Bubbler?

2. Dealing with Stress

Minimizing stress is key in ensuring your molly fish’s health and normal breathing. Here are a few practical steps to consider:

  • Gentle Handling: Limit handling to necessary instances like tank cleaning, and always use a soft net to reduce stress on your molly fish.
  • Stable Environment: Keep changes in water temperature and pH within a 1-2 degree/0.1-0.2 range per day to prevent stressful conditions.
  • Comfortable Habitat: Provide ample hiding places and swimming space. A good rule is to have at least one hiding place per fish.
  • Balanced Diet: Feed a mix of commercial flake food and live or frozen foods like brine shrimp or bloodworms for a balanced diet, reducing dietary stress.
  • Peaceful Tank Mates: Introduce only compatible, non-aggressive species to the aquarium. Molly fish typically enjoy the company of guppies, platies, and tetras.

Here are some peaceful species to keep with mollies:

  • Cherry Barb (Puntius titteya)
  • Harlequin Rasbora (Trigonostigma heteromorpha)
  • Zebra Danio (Danio rerio)
  • Celestial Pearl Danio (Danio margaritatus)
  • Otocinclus Catfish (Otocinclus spp.)
  • Pygmy Corydoras (Corydoras pygmaeus)
  • Neon Tetra (Paracheirodon innesi)

On the other hand, these aggressive species should not be mixed with mollies:

  • Tiger Barb (Puntigrus tetrazona)
  • Red-Tailed Black Shark (Epalzeorhynchos bicolor)
  • Siamese Fighting Fish/Betta (Betta splendens)
  • Jewel Cichlid (Hemichromis bimaculatus)
  • Jack Dempsey Cichlid (Rocio octofasciata)
  • African Cichlids (Various species from the Cichlidae family)
  • Green Terror (Andinoacara rivulatus)

Also Read: 19 Great Neon Tetra Tank Mates

3. Resolving Temperature Increases

Maintaining a comfortable water temperature is essential to your molly fish’s wellbeing. Here are some tips to manage temperature increases:

  • Regulate Tank Temperature: Keep the tank temperature stable within 70-82°F (21-28°C), using a reliable aquarium heater and thermometer. My recommendation: Orlushy Submersible Aquarium Heater (link to Amazon).
  • Avoid Rapid Fluctuations: When changing water, ensure the new water is within 1-2 degrees Fahrenheit of the tank water to prevent temperature shock.
  • Proper Cooling Mechanisms: During hot weather, use cooling fans or chillers to keep the tank temperature within the suitable range.
  • Monitor Equipment: Check lighting and other equipment regularly for overheating. Use LED lights which generate less heat.
  • Enhance Aeration: With every 10°F increase in temperature, the oxygen solubility drops by about 20%. Counteract this by increasing aeration during warmer periods.

Also Read: Molly Fish Temperature

4. Addressing Ammonia Surges

Maintaining water quality is vital for the health of your molly fish, especially in controlling ammonia levels. Here are actionable steps you can take:

  • Feed Appropriately: Feed molly fish no more than they can consume in 2-3 minutes, twice a day, to prevent food waste and limit ammonia production.
  • Remove Dead Organisms: Immediately remove any dead plants or animals, as these decompose quickly and raise ammonia levels.
  • Effective Filtration: Use a biological filter that can break down ammonia. A well-maintained filter can keep ammonia levels close to zero.
  • Regular Water Changes: Perform weekly 20-30% water changes to prevent the build-up of harmful substances like ammonia.
  • Proper Tank Cycling: Before introducing molly fish, ensure the tank is cycled properly, which can take 4-6 weeks, to establish beneficial bacteria that consume ammonia.

Also Read: Molly Fish Tank Setup

5. Handling Illness

If your molly fish is sick and breathing rapidly, professional advice might be needed. Meanwhile, consider these steps:

  • Watch for Disease Signs: Monitor molly fish daily for signs of disease like changes in color, appetite, or behavior, and act promptly at the first sign of trouble.
  • Treat Parasites: For parasitic infections, over-the-counter treatments like copper-based medications can be used. Always follow dosage instructions carefully. My recommendation: Hikari Prazipro (link to Amazon).
  • Fight against Bacterial Infections: Tetracycline or erythromycin, which are antibiotics or antibacterial agents, can assist in combating bacterial illnesses. You can also use the API MELAFIX (link to Amazon).
  • Maintain Water Quality: Regular testing and maintenance to keep pH between 7.5-8.5, ammonia and nitrite at zero, and nitrate below 20 ppm can help prevent many illnesses.
  • Ensuring Adequate Nutrition: Give molly fish a diverse range of food to strengthen their immune system. Include vitamin-rich brine shrimp along with top-quality flake or pellet food in their meals.

Also Read: 15 Molly Fish Diseases & Their Treatments

Steps to Prevent Rapid Breathing in Molly Fish in the Future

In order to avert future episodes of rapid breathing in your molly fish, it’s essential to offer them a wholesome living environment and proper attention.

You can dramatically cut down on stress and enhance their habitat’s healthfulness by maintaining a good water quality, temperature, tank occupancy, and balanced diet.

Here are some effective measures:

  • Water Quality Upkeep: Regularly check the water’s parameters. Strive to retain a pH of 7.5-8.5, have zero ammonia and nitrite, and keep nitrate levels under 20 ppm. I do that with the API FRESHWATER MASTER TEST (link to Amazon).
  • Temperature Management: Keep the temperature steady within the molly fish’s preferred range of 70-82°F (21-28°C) with the help of an aquarium heater and a dependable thermometer.
  • Population Regulation: Refrain from overstocking the aquarium. Stick to the rule of thumb of 1 gallon of water per inch of fish to guarantee sufficient oxygen for your molly fish.
  • Diet Balance: Serve your molly fish a balanced diet that encompasses top-notch flake food and additional live or frozen foods such as bloodworms or brine shrimp, in measured quantities.
  • Routine Observation: Keep an eye on your molly fish every day for signs of distress or sickness, like shifts in color, appetite, or behavior, and respond quickly if any irregularities are spotted.


For those of you who are short on time, here is a quick overview of what I discussed earlier:

  • Rapid breathing in molly fish can be caused by insufficient oxygen levels, which can result from factors such as poor filtration, overcrowding, and low oxygen absorption by plants at night.
  • Stressful conditions, including rough handling, rapid changes in water parameters, aggression from tank mates, and inadequate habitat, can lead to molly fish breathing rapidly.
  • High water temperature outside the recommended range, rapid temperature fluctuations, inadequate cooling mechanisms, overheated equipment, and insufficient aeration can all contribute to molly fish exhibiting rapid breathing.
  • Elevated ammonia levels caused by overfeeding, decaying organisms, poor filtration, rare water changes, or an uncycled tank can result in molly fish breathing faster.
  • Sickness or diseases, including infectious diseases, parasitic infections, bacterial infections, poor water quality, and poor nutrition, can lead to rapid breathing in molly fish. Prompt professional advice should be sought in such cases.