Guppy Fin Rot: Main Causes & Symptoms And Quick Prevention

Guppy Fin Rot
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Last Updated: March 22, 2023 by Dave Gibbins

Guppies make excellent community fish due to their peaceful temperament and hardy nature. Moreover, they have colorful, long flowing tails that people find relaxing to watch as they swim around the aquarium. 


These tails and fins are prone to developing guppy fin rot. But what is guppy fin rot? What causes it? And are there ways to treat or prevent it? 

Read on to find these answers. 

What Is Guppy Fin Rot? 

Fin rot is an infection that affects not only guppies but other fish species. You can easily treat it in the early stages, but if left untreated, it becomes fatal to guppies.

Guppy fin rot is caused by fungal or bacterial infection. Pseudomonas fluorescens is the bacteria responsible for this infection. It is present in most aquariums and only infests a fish’s body under certain conditions. 

Guppies with bacterial infections have uneven and rugged fins. 

On the other hand, a fungal infection fin rot appears more even with white spots on the fins. Both infections affect all fins, including pectoral, dorsal, anal, and pelvic fins. At times, some guppy fish may exhibit signs of both bacterial and fungal fin rot.

You should determine whether your guppies have bacterial or fungal fin rot during treatment. 

Causes Of Fin Rot In Guppies

Damaged Or Injured Fins

Guppies are prone to hurting and damaging their long, thin, flowing fins on sharp edges in the fish tank. When this happens, they become more susceptible to catching infections. In addition, if guppies sustain injuries from aggressive bullies, they can also become ill.

Poor Water Quality

Poor water quality also causes infection and illnesses. Guppies enjoy spending their day eating, and this behavior results in a high bioload. If this waste is not regularly cleaned, it will pollute the water with high amounts of ammonia and nitrites. This, in turn, makes guppies prone to fin rot. 

Fluctuating Water Conditions

Guppies are happier when their aquarium water temperature and pH levels remain stable. Even so, they are hardy fish that can survive in temperatures slightly lower or higher than their ideal range. 

However, if guppies are constantly exposed to fluctuating temperatures and pH, they become stressed and more susceptible to diseases. 


Consistent stress weakens a guppy’s immune system. Stress could result from poor water quality, aggressive tank mates, or fluctuating water temperatures and pH. 


Overcrowding makes guppies prone to fin rot due to three reasons. First, when your aquarium is overstocked, your guppies will have less space to move around, swim, hide, and play. This will push these peaceful fish to become aggressive and start fin nipping. The injuries on the nipped fins make it easy for the guppies to catch infections that cause fin rot. 

Second, an overstocked fish tank will have increased bioload, harboring harmful bacteria growth. These bacteria weaken your guppies’ immunity.

Lastly, an overcrowded tank becomes a stressful environment for your guppies. Stressed fish are more prone to developing fish diseases. 

Symptoms Of Fin Rot In Guppies

Fin rot is categorized into three stages: mild fin rot, major fin rot, and severe fin rot. Each category has its severity and distinct symptoms. For better insight, let us look at the symptoms of each stage. 

Mild Fin Rot

This is the first stage of fin rot. Guppies in this stage exhibit these symptoms: 

  • The tips of the fin begin to change color or become darker. The fins may have a gray, white, or brown color. 
  • Fin edges are slightly tattered. 
  • The tips of the fins may appear red and sore.
  • The fins may have signs of irritation.
  • The rot appears on the edges of the fins.

Major Fin Rot

Most fish keepers do not notice fin rot in the mild phase. When this happens, the infection advances to become major fin rot. If your guppies are in this stage, start immediate treatment or risk further weakened immunity that will bring other illnesses.

The symptoms to watch out for are:

  • A larger portion of the fins rots away.
  • Larger parts of the fins appear discolored or darker.
  • The fins will have a white fuzz if your guppy has a fungal infection.
  • The fins may start to die completely. 
  • Parts of the fins will fall off. 

Severe Fin Rot

As you can tell, severe fin rot results from not treating fin rot at its first two stages. The infection usually progresses at this stage, and it is practically impossible to save your other fish. Severe fin rot is also known as body rot. 

Symptoms include: 

  • Your guppy’s body starts to rot.
  • Guppies’ fins are completely decayed or eaten away. 
  • For fungal infection, you will notice white fuzz where the fins were.
  • Loss of appetite
  • Guppies gasping for air due to troubled breathing
  • Lethargy

How To Treat Guppy Fin Rot

The severity of the infection will determine whether you can treat fin rot or not. You can easily treat guppy fin rot in the mild or major stage. However, if your aquarium fish are exhibiting signs of severe fin rot, there may be little you can do at this point. 

Also, check whether your guppies are suffering from fungal or bacterial fin rot. This will help you choose the correct treatment.

During treatment, remove the infected fish from the original tank and into a quarantine tank to prevent passing the infection to other healthy fish.  

How To Treat Mild Fin Rot In Guppies

You can treat minor fin rot in guppies by doing the following: 

Step 1: Clean the gravel. Gravel keeps waste and debris that feeds the bacteria responsible for fin rot. By cleaning it, you remove this waste and prevent further infections. 

Step 2: Perform a 25% water change to add fresh, clean water. 

Step 3: Monitor that the water parameters match a guppy’s living conditions. This includes the water temperature, pH, hardness, chlorine, ammonia, and nitrite levels. 

Step 4: Once you’ve made the tank clean through steps 1 to 3, treat your guppies with an aquarium conditioner or a stress coat. You can consult your vet about the best medication. 

Step 5: Follow the specified instructions on the label.

Step 6: Remove the carbon filter from the tank as it can render the medication ineffective.

Step 7: Monitor the progress of your guppies. The condition should improve in a few weeks.

How To Treat Major Fin Rot In Guppies

If your guppies surpass the mild fin rot phase, you should administer immediate treatment to prevent the infection from worsening. 

Here is how to treat fin rot:

Step 1: Remove the sick fish from the main tank and into a separate tank. Use water from the main tank to acclimatize the guppies.

Step 2: Carry out a complete water change in the original tank and clean all the surfaces present. Doing so will reduce and prevent the recurrence of fin rot. 

Step 3: Mix aquarium salt with pure water according to the instructions. Once dissolved, add it to the quarantine tank.

Step 4: Perform a daily complete water change when using aquarium salt.

Step 5: Use this treatment for as long as the label recommends. The duration often lasts a week.  

How To Treat Severe Fin Rot

When guppy infection gets to the severe stage, there is little you can do to cure fin rot. But as a fish owner, you cannot just stand by and watch your guppy fish waste away. 

Here is what you can do to treat severe fin rot:

Step 1: Set up a separate quarantine tank for the infected fish.

Step 2: Add an air bubbler to keep the aquarium oxygenated. 

Step 3: Find strong medication for the infection. Fish owners and professional vets recommend API FURAN-2 for bacterial fin rot and API Pimafix for fungal infection. These medications can lower oxygen levels in the aquarium, hence the need for an air bubbler. 

Step 4: Make 100% water change daily in the quarantine tank before adding the medication. This will prevent you from overdosing and poisoning your guppy fish. 

Step 5: Perform a 100% water change in the main tank. This will ensure your healthy fish do not get the infection.

Step 6: Monitor improvement in your guppies. If your sick fish recover from the infection, move them to the original tank. 

How To Treat Bacterial Fin Rot In Guppies

Antibiotics are the most effective way to cure bacteria diseases. The following are your best options when curing fin rot in guppies. 

Aquarium Salt

Aquarium Salt

Aquarium salt is often used to treat infections in freshwater aquariums as it is non-toxic to fish. 

Aquarium salt helps boost a fish’s immune system to resist and fight infections. Moreover, the salt increases their osmotic pressure, which reduces stress in guppies. This makes them less prone to infections. 

When using aquarium salt, add one teaspoon for every gallon of water. Nevertheless, always perform a complete water change when adding salt. A salt overdose can damage your fish’s gills and skin. 


This antibacterial medication treats fin rot, inflamed gills, and other bacterial diseases. It is readily available in local pet stores. But as effective as the medication is, follow the provided instructions about dosage since it causes sensitivity to some fish. 

Here is a YouTube video about this natural treatment:


This broad-spectrum antibiotic is most effective in treating gram-negative bacteria and gram-positive bacteria. You can use this medication to cure pathogenic bacteria diseases like fin rot, ulcers, Popeye, and septicemia. 

Furan-2 does not cause sensitivity on scale-less fish. But, it should only be used in a quarantine tank since it disrupts the populations of healthy bacteria in a tank. 

You should follow the following steps when using the above antibiotic to treat body rot.

Step 1: Set up a hospital tank for your sick fish. 

Step 2: Mix your preferred antibiotic with water according to the instructions. Add the dissolved solution into your hospital tank. 

Step 3: Perform a daily 100% water change in the quarantine tank as your guppy fish improve.  

Step 4: Clean the original clean tank and perform a complete water change. 

How To Treat Fungal Fin Rot In Guppies

If your guppies show signs of a fungal infection, look for fungus treatment medication. Most fish owners use methylene blue to cure fungal fin rot and other parasitic infections. 

Pimafix, a plant-based medicine, also cures fungal infections. Be extra careful with the dosage to avoid hurting your guppy fish’s slime coat. Also, remove activated carbon from the filter as it renders the medication ineffective. 

Here is what to do when using methylene blue:

Step 1: Isolate the infected guppy fish in a hospital tank.

Step 2: Perform a daily 30% water change to improve water quality and reduce stress on your sick guppies. 

Step 3: Include a 30-minute methylene blue bath every day. The bath kills bacteria on the fish’s body and reduces fin rot. It also promotes the tissues absorbing oxygen better.

Step 4: Repeat the above steps for two weeks until the infection is cured. 

How To Prevent Fin Rot In Guppies

Did you know you can prevent your aquarium fish from catching fin rot? You can prevent fin rot by doing the following: 

1. Provide Optimal Water Conditions

Your guppies will be free of fish diseases if you maintain stable water temperatures, pH, and low ammonia, nitrate, and nitrite levels. 

2. Clean Tank Regularly

These tropical fish will thank you for keeping their tank clean.  A clean tank hosts fewer bacteria which results in infections. Keep in mind that your cleaning schedule will mainly depend on how many fish are in the tank and the tank size. A small, overstocked will need more cleaning sessions than a bigger tank. 

3. Perform Frequent Water Changes

You create a healthy environment for your guppies by performing frequent water changes. The frequency of the water changes will also depend on the stocking of the tank and its size. 

4. Avoid Overcrowding

Keeping the right number of fish will prevent your aquarium fish from getting aggressive and developing fin nipping behavior. Moreover, there won’t be too much bioload to lead to harmful bacteria growth.

5. Avoid Aggressive Tank Mates

Guppies are peaceful community fish that should live with other peaceful tank mates. If you house your guppies in the same aquarium with aggressive mates, they will become stressed and weaken their immunity. 

6. Invest In A Quality Filter

A high-quality filter will help get rid of ammonia, debris, and fish waste to maintain water chemistry and quality. This will keep your fish healthy and happy. 

7. Feed High-Quality Food

Guppies develop a strong immune system to fight infections when they eat high-quality food that meets their dietary needs. Guppies are omnivores who enjoy eating meaty foods and plant matter. 

8. Provide Hiding Places

Guppies love a tank with hiding spots. These spots offer privacy, comfort, security, and hiding places when they feel stressed. 

9. Quarantine New Fish

Before you introduce new tank mates, ensure you place them in a quarantine tank to ensure they do not harbor diseases. 

Is Fin Rot Contagious? 

Yes. Guppies infected with fin rot can spread it to other fish, infecting the entire tank if you do not act fast.  If some guppies are infected, move them to a separate tank and perform a 100% water change in the community tank to prevent more infections. 


Guppy fin rot is a preventable fish disease. If you keep your guppies in a clean, healthy environment, they will be less prone to this disease. 

Nevertheless, if your guppies catch this illness, you can treat it in the mild and major stages. In addition, discern whether the infection is bacterial. But do not expect the fins to grow back after successful treatment.