Neon tetra cotton mouth despite treatment?


Hi all,

One of my neon tetras has some white growth on his lower lip that is very slowly growing bigger.

What is the water volume of the tank? 10l
How long has the tank been running? 1 year
Does it have a filter? Yes
Does it have a heater? Yes
What is the water temperature? 26C
What is the entire stocking of this tank? 2 neon tetra, 1 ramshorn snail

How often do you change the water? Once per week
How much of the water do you change? 40-50%
What do you use to treat your water? Prime water conditioner
Do you vacuum the substrate or just the water? Just water

*Parameters - Very Important
Did you cycle your tank before adding fish? Yes
What do you use to test the water? Interpret easy test dip kit
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”
Tested today, last water change 1 week ago
Ammonia: 0mg/l
Nitrite: 0
Nitrate: 0
pH: 6.8-7.2

How often do you feed your fish? Once per day
How much do you feed your fish? Small amount
What brand of food do you feed your fish? JNL NovoBel tropical flakes
Do you feed frozen or freeze-dried foods? No

Illness & Symptoms
How long have you had this fish? 1 year
How long ago did you first notice these symptoms? 3 weeks 2 days
In a few words, can you explain the symptoms? White growth on lower lip, growing in size slowly
Have you started any treatment for the illness? Yes eSHa 2000 fungus, finrot and bacteria treatment 2x complete set of 10 days
Was your fish physically ill or injured upon purchase? No
How has its behavior and appearance changed, if at all? No, good mood, eating well and playing with second fish

We moved on 3 weeks ago. The day after the move I discovered the white spot on the lower lip. Aquarium shop suspected physical injury due to transport but gave the eSHa 2000 fungus, finrot and bacteria treatment just in case to make sure. I completed 10 days of treatment twice, but no improvement. Does not get significantly worse, but definitely a little bit bigger than before. Looks like the lower lip is split and white fluff in between.

I suspect it’s a physical injury since the treatment did not help, nonetheless after 3 week I would suspect he would be better. He seems happy though and does not show and signs or symptoms of stress or pain.

Any ideas what this could be and how I can help him?



hm strange how the meds haven't really helped, perhaps try another med as some strains of columnaris are resistant to some antibiotics/antibacterial meds (if it is columnaris) or try a med specifically for fungal infections however I'm not sure which one this is so I'll have to leave this for someone else to answer, good luck to you and your little fishy


Some say it is a part of the neon specific strain of Columnaris. My idea is it is a viral issue (Iridovirus) which causes these lumps.

In the hundreds of cases no med worked against it. It seems not to be very lethal and not contagious to other species.

So acceptation and keeping the water clean is the only way.
  • Thread Starter


Thank you so much for your answers. This reassured me greatly. It’s sad that I probably can’t do anything to help him, but as long as he is not unhappy I’ll just make his life as comfortable as possible.
Thank you!

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