How many gallons is the tank please?
How many fish and which type?
Water stats in ammonia, nitrite, nitrate, and ph?
How did the other Neons die please?
Does the Neon show any of these signs.
Is the fish still eating.
What does it look like when the fish goes to the toilet.
Red area will look bleached out. Bleached out patches.
Blue area will have a milky substance, or turn a golden yellow colour.
Black lining around the tail area.
Fish will leave shoal.
Fish will become restless.
Fish can also look wasted away. Very thin.
Lumps on belly that go to a point.
Swimming in an odd manor.
Later stages dropsy, popeye.
The fish is still eating just like it normally does
It's red area does have a bit of discoloration, it is kinda pale in some spots.
His stripe is definitely still blue, though not quite as bright as it should be, just enough to be able to tell a difference.
It did leave the other tetras behind every little bit, but I just put them in 2 days ago so it could have just been getting used to having more of its own kind again I guess.
It doesn't really look thin but it does look like it could eat a little more.
I don't see the other symptoms though and I don't have the answer to the second one. I have separated it from the other fish now. Also, it has a spot just above it's mouth that it keeps bumping into the wall of the tank.