Can we have your exact parameters please? It’s easier to tell if something might be wrong with the actual informationIt’s hard to see what your referring to because the picture is so blurry, can you get a clearer one? Very hard to see poor camera on phone
What are your parameters? (Ammonia, nitrite, ect) all fine
How long have you had the fish? About 4 months
Have you added anything new to the tank in the last two weeks? Nope
How often do you do water changes and how much do you change at a time? Weekly 40%
Thank youWhite lumps on the mouth of neon tetras is something we are coming across more frequently of late. It seems to be a viral infection affecting neons, so there's no cure. The fish behave normally until the lump gets so big it stops them eating, and which point they should be euthanised.