Columnaris In Guppies (Treatment, Causes, Prevention)

Fortunately, columnaris in guppies isn’t very common. However, if it does strike, then you’ll need to make sure you’re treating it quickly. If left untreated, it can become fatal and spread to the rest of the fish in your tank,

However, you’ve come to the right place. If you think that your guppy is suffering from columnaris, then this article is going to teach you exactly how to treat it. Not only that, but you’ll also learn what causes it, the symptoms, and most importantly, how to prevent it.

So keep reading to find out everything you want to know about columnaris in guppies!

What Is Columnaris?

Columnaris is a bacterial infection that can affect any fish when their immune system is compromised. Generally, it’s always present in a tank; however, it’s only when a fish becomes weak that it generally infects them.

As well as columnaris, it is also known by other names, including cottonmouth disease, cotton wool disease, and saddleback disease.

If you hear these names, then they are all in reference to the same illness.

What Causes Columnaris In Guppies?

As you now know, columnaris is generally always present in a fish tank. And it only strikes when a guppies immune system is compromised. So when you ask, “what causes columnaris?” the real question is, “what weakens your guppy’s immune system?”

Here are a few of the things that will weaken your guppy’s immune system.

Poor Water Quality

Poor water quality is one of the biggest factors that will determine whether your guppy has a strong or weak immune system. Some of the causes of poor water quality are:


Overstocking is when the amount of fish in your tank exceeds the capabilities of the tank or filter. When your tank is overstocked, the filter is going to have a much harder time keeping up with the excess waste.

If it can’t keep up with the excess waste, then the water is going to become a breeding ground for bacteria.

And on top of this, when there are too many fish in a tank that isn’t big enough, none of the fish will have enough room to swim. This will also stress your guppies out as they like to be able to swim freely.

(Find out how many guppies you can keep in a 5 gallon, 10 gallons, and 20-gallon tank.)

Fluctuating Water Temperatures & pH Levels

You should also note that if the water temperature and pH levels fluctuate too much, it’s going to have a disastrous effect on your guppy’s immune system. (Want to know the ideal pH level for guppies?)

This is one of the reasons it’s so important to keep a heater in your tank and make sure that you’re checking the tank’s water parameters regularly. (Everything you need to know about guppies and heaters.)

And if the water temperature fluctuates too much, then it can often end up becoming fatal pretty quick for your guppies before any disease is even able to take hold.

Not Cleaning The Tank/Changing The Water Enough

And lastly, if you’re not cleaning your tank and changing the water often enough, it’s going to lower the water quality in your tank.

You should be changing the water in your tank weekly/bi-weekly depending on the size of the tank and how many fish are in it.

(It also helps to make sure you have a filter for your guppy tank.)

Poor Diet

Without a good diet, your guppy is going to be unable to keep its body strong and energized. It will begin to get weak, and obviously, its immune system will weaken as well.

Even if you’re feeding them enough, if you’re not feeding them high-quality food, then they’re still not going to be as strong as they should be.

(Find out the best foods for guppies and what they should eat.)

Bullying And Harassment

Bullying and harassment will also significantly weaken your guppy’s immune system. If your guppy is constantly being bullied then they’re less likely to eat, they’ll always be stressed, and they won’t be able to rest properly in the tank.

(Find out more about whether guppies are aggressive and whether they fight.)

And this isn’t even if you take into account fish that fin nip or bite their fins. When this happens, the damage will also massively weaken your guppies’ immune system and increase the chance of guppies suffering from fin rot.

If your guppy is getting attacked, then the bacteria can enter their body via the cuts on sores on their skin as well.

Shipping And Handling

Shipping and handling are going to be an extremely stressful time for your guppy. Not only is the journey itself a stressful experience, but the change of water parameters from their old tank’s water to their new tank’s water is also going to stress them out as well.

This is one of the reasons you want to slowly acclimatize them to the tank by letting them sit on top of the water in their bag for a while. This way, the water they’re in slowly changes the temperature of the water in your tank. And by letting water into their bag slowly, they’re going to become used to the water parameters of your tank.

Passed By Equipment

The bacteria that causes columnaris is also going to contaminate everything it touches as well. If you’ve moved a guppy to your quarantine tank, you should try to avoid using the same equipment between the quarantine tank and the main tank.

If you do this, you could end up increasing the amount of columnaris in the water, increasing the chances of other fish-catching it as well.

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What Are The Symptoms Of Columnaris In Guppies?

Fortunately, if you’re guppy is suffering from columnaris, you’re going to be able to spot it easily. The main symptom of columnaris (as you can guess from its other names) is cotton-like growths on their body. Especially around their mouth (however, it can happen anywhere).

Here are some of the other symptoms.

Frayed Fins

One of the earliest signs of columnaris that you’ll see is frayed fins. The very edges of the fins will begin to look tattered and slightly damaged. However, make sure you don’t mistake this with fin rot, which is another disease that can affect guppies (but will need a different treatment).

Ulcers And Sores

After noticing that your guppy’s fins are looking a bit frayed and tattered, you may also notice that ulcers and sores begin to appear on their body.

This is the best way to differentiate between fin rot and columnaris in the early stages.

White Cotton Like Growths

Next, the cotton-like growths that give columnaris its names begin to appear. As previously mentioned, this can happen anywhere on their body, but it’s much more likely to happen around their mouth and gills. As well as this, it can also grow along their back, resembling a saddle.

Remember, though; other diseases can cause white growths on your guppy, including ich.

Rubbing Against Things

This can happen at any stage of columnaris and may even happen before you notice the growth. Your guppy will be aware that there’s an infection on their skin, so they’ll begin rubbing their bodies against things in order to try and remove it.

This can also be one of the reasons that ulcers and lacerations appear. And the more lacerations that appear, the more bacteria can infect your guppy.

You May Notice Mucus

Certain areas of your guppy’s body, including their gills, mouth, head, and the dorsal area will begin to have mucus on them as well. This is because your guppy’s immune system is trying to remove the bacteria as best it can. However, unfortunately, this won’t work.

The Gills Will Turn Brown

In the later stages of columnaris, your guppy’s gills will turn brown. At this stage, it’s going to be a lot harder to treat. The reason the gills are turning brown is that the cells are starting to die, and necrosis is setting in.

As well as the gills going brown, you’ll also notice that your guppy is going to have trouble breathing and may begin breathing rapidly to try and get more oxygen in.

Their Mouth Will Deteriorate

As the columnaris progresses, your guppy’s mouth will begin to swell, and in some cases, it may end up also beginning to rot off.

Other Symptoms

Aside from these symptoms, you may also notice lethargy, a lack of appetite, staying away from other fish, and hiding. In the most extreme cases of columnaris, you may even notice that your guppies head begins to rot away.

How Do You Treat Columnaris In Guppies?

Fortunately, if your guppy is suffering from columnaris, then it’s definitely treatable. And if you catch it early enough, then your guppy will make a full recovery! Here’s how to treat columnaris in guppies!

Step 1: Quarantine Your Guppy

The first thing you’re going to want to do is quarantine your guppy. Quarantining your guppy has two benefits. First of all, it’s going to help reduce the chance of columnaris spreading to other fish in your tank. Secondly, it’s going to give your guppy a nice place to recover away from the stress of other fish.

And on top of this, you’ll also need to quarantine your guppy so you can medicate them properly. If you’re adding the medicine to your main tank, then you’ll also be medicating fish that aren’t sick, which isn’t good. And a small quarantine tank is much easier to dose than a bigger tank.

Test The Water In The Tank

You should test the water in your quarantine tank to make sure it’s perfect before dosing with medication. If the water parameters aren’t perfect, then your guppy is going to be stressed, which is going to result in the columnaris potentially doing more damage.

Using an API Master Test Kit. Test the pH and make sure it’s between 6.8-7.8. Next, test the ammonia, nitrate, and nitrite levels. The nitrite and ammonia levels should be 0ppm, and the nitrate level should be below 20ppm. If they’re not, then use an ammonia neutralizer to remove any excess ammonia. Once the ammonia levels fall, the other two will drop as well.

Slowly Lower The Temperature In Your Tank

Now that the water parameters in your tank are perfect, you should begin lowering the temperature of the water. Columnaris loves the heat, so turning down the water temperature is going to slow down its growth as well as kill some of it off.

The temperature shouldn’t exceed 75°F, and if possible, you should try to get it as low as 72°F. Just remember that lowering the temperature shouldn’t be done all at once, but it should be a gradual process. You should only lose 1°F every few hours.

If you adjust the temperature too quickly, then your guppy could suffer from temperature shock,’ which is often fatal.

Begin Dosing With Medication

Now the next step is to begin dosing with medication. However, before you dose your tank with medication, make sure you’re removing the chemical filter media from the tank; otherwise, it could stop the medication from working.

When choosing medication, you’ll need to choose medication designed to fight bacteria specifically. Furan-2 And Kanaplex are often recommended.

When you’re using these medications, make sure you always read the instruction on the bottle before dosing. If you get the dosages wrong, then you may end up doing more harm than good to your guppies.

If your guppy is in a severe condition, then you may need to do back-to-back treatments to help them. Just make sure this doesn’t last for more than two days.

And remember, this should also be a last resort as it’s going to put a lot of stress on your guppy’s body.

How To Prevent Columnaris In Your Guppies

Preventing columnaris from happening in the first place is going to be so much better than having to treat your guppy for it. And fortunately, prevention is quite easy. Here are some of the ways you can prevent columnaris in your tank.

Keep The Water Quality Good

The first thing you should be doing is making sure the water quality remains consistently good. To do this, perform frequent water changes and clean the tank.

On top of this, remove any wasted food that your guppy doesn’t eat, and make sure you’re not overstocking your tank either. As a rule of thumb, you should only be adding 1″ of fish per gallon of tank water. So a 10-gallon tank can hold 4 guppies who grow 2 and a half inches in size each.

Quarantine New Fish

You should also quarantine any new fish before adding them to your tank. Even if they don’t have any symptoms, they could still be sick. And even if they don’t give your fish columnaris, they could give them another illness, weakening them and opening them up to the possibility of suffering from columnaris.

You should quarantine new fish for 2 weeks and watch them for any signs of illness.

Remove Aggressive Fish

If there are aggressive fish or bullies in your tank, then you should separate them from the other fish in your tank. Aggressive fish are going to weaken the immune system of all the fish in your tank by damaging them and stressing them out.

If you have a fish that is constantly aggressive, your best bet is to try and take them back to the shop or move them to a different tank.

Feed Your Guppies A High-Quality Diet

A good diet is essential for keeping your guppy healthy. Without the right nutrients, their body will become weak, and their immune system could be compromised.

If you’re not sure what food to give your guppies, then here are some of the best choices.


As you can see, columnaris in guppies can be extremely serious if you don’t treat it quickly enough. However, if you catch it early and treat it quickly, your guppy is likely to make a full recovery.

And, of course, the most important thing to remember is that prevention is better than treatment. You should always be keeping the conditions in your tank great to prevent columnaris from happening.

About the author

Hey! I'm Antonio!

Betta fish keeper for over 6 years now! Since owning a betta I've also housed all kinds of tropical fish, and have seen all manner of problems and how to look after them!

If you need any advice you can always message me or better yet join the Facebook group where a community can answer your questions!