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How To Treat Cotton Mouth In Neon Tetras!

With neon tetras being such a beginner friendly fish to keep, a huge number of people new to fish keeping choose them as one of the fish species in their very first tank.

This means that many of the common issues that fish keepers go through with their fish are experienced with the neon tetras before the fish keeper moves on to other species.

This means that we see a huge number of questions about common conditions in neon tetras and how to fix them.

One of the more commonly asked questions that we have been seeing from the community recently is based around treating cotton mouth in neon tetras.

Now, for the most part, cotton mouth does tend to be easy to treat provided you catch it early so it’s not usually something that you have to worry too much about and it’s great to see so many people new to the hobby reaching out and asking for ways that they are able to help their fish.

Due to seeing so many people reaching out and asking about treating cotton mouth in their neon tetras, we wanted to publish our own dedicated article.

Our hope is that we will be able to answer as many of the common questions we see about neon tetra cotton mouth in one place and help as many of our readers as possible.

What Is Cotton Mouth in Neon Tetras?

Cotton mouth, also known as cotton wool disease and columnaris is a condition that affects fish and results on growths that look like cotton wool.

These growths can occur on the mouth of your fish as well as on their body, tail, and fins too with treatment usually being easy.

Many people new to fish keeping are often shocked to discover that their fish have cotton mouth as they work so hard to keep their tank clean but cotton mouth is a very common problem.

Even experienced fish keepers can have problems with it at times and having problems with cotton mouth in your tank does not mean that you have done anything wrong or that you are a bad fish keeper.

We have seen some people think that fish keeping is not for them due to having their first set of fish like neon tetras have problems with cotton mouth after putting a ton of time and effort in to protect their fish.

You can do everything correct and still end up with a cotton mouth breakout in your tank as it only takes a single spore to land in the right place for everything to start so it is easy to see why fish keepers of all levels of experience have problems with cotton mouth.

“Neon Tetra Fish (0024)” by MrJoshGeddes is licensed under CC BY-NC 2.0. To view a copy of this license, visit

What Causes Cotton Mouth in Neon Tetras?

Cotton mouth in neon tetras is causes by a breakout of the Flavobacterium columnare bacterium and it can easily be accidentally added to a tank when adding new fish, rocks, plants, substrate, and live food.

It is very common and is one of the main reasons that most people will quarantine anything prior to adding it to their main tank to check if there are any problems with parasites or bacteria such as Flavobacterium columnare that causes cotton mouth.

If you are planning to add new plants, rocks, or substate then a dip treatment is often able to deal with any bacteria or parasites on the new addition prior to adding it to your tank.

You usually are not able to do this with fish though so most people will add them to a quarantine tank prior to adding them to their main aquarium.

Some people will give their fish salt baths or methylene blue baths to try and prevent any outbreaks of bacteria in their tank like methylene blue to reduce the chances of their fish having problems with cotton mouth.

We usually don’t recommend anything like this unless your neon tetras are already having problems with cotton mouth as it is generally better to avoid having to give your fish any type of cleansing bath unless you really have to.

How Do You Treat a Cotton Mouth Neon Tetra?

Cotton mouth is usually very easy to treat in neon tetras with there being a number of treatment options on the market that work well.

Both Melafix and Primafix can both work well at treating but there are a number of other suitable treatments on the market too.

The majority of beginner fish keepers should carry a bottle of either Melafix or Primafix in their fish keeping supplies anyway due to both products being excellent treatment options for a range of common issues.

Both tend to work well at treating cotton mouth in your fish with the main difference between the two being that the active ingredient in both formulas is slightly different and slightly stronger in Primafix.

Both products are around the same price point while also being very beginner friendly and offering an easy to follow dosing guide that you can follow specific to your tank set up on the label of the treatment.

This ensures that you are able to quickly, easily, and cheaply treat the cotton mouth in your neon tetras and help get them back to full health quickly.

Is Cotton Mouth in Neon Tetra Contagious?

Cotton mouth is highly contagious and can easily transfer between fish species too so your neon tetras with cotton mouth can easily transfer it to other fish in your tank.

It is usually recommended that you try to quarantine any fish that have cotton mouth for treatment but if you are unable to quarantine them, treating the full tank is often recommended.

Keep in mind that this will depend on the setup of your tank as some fish and live plants are more sensitive than others and may not react well to cotton mouth treatments being added to their water supply.

For the most part though, neon tetras do tend to be easier to catch and can be quarantined in much smaller tanks than many other fish species allowing you to treat them while presenting minimal risk to your other fish.

Some fish keepers will still add a small dose of something like Melafix or Primafix to their main community tank after a cotton mouth outbreak even if they do manage to quarantine the fish suffering from cotton mouth.

This helps to minimise the risk of any Flavobacterium columnare bacterium in the water supply of your main tank taking hold of the health fish and causing a secondary cotton mouth outbreak.


That brings our article going over treating cotton mouth in neon tetras to a close. Although cotton mouth is a serious illness, it is generally very easy to treat provided that you catch it early enough. Some fish may have long term scars after having cotton mouth due to the sores scaring them but for the most part, the majority of fish should make a full recovery provided you were able to catch the cotton mouth outbreak early enough in your neon tetras.