Wow, he looks really pale, too
. Is his coloration really like that? You said it was normal but it seems paler then it should be.
As much as I hate to say it, he might have Neon Tetra Disease
.
Symptoms include restlessness, pale coloration, a "lumpy" body, difficulty swimming, a curved spine (at advanced stages), and bloating/secondary infections like
fin rot. Infected fish will often stop schooling with the others and swim strangely.
It's caused by
Pleistophora hyphessobryconis, parasitic spores.
Neon tetras are usually infected when they eat or pick at a dead fish or eat live food with the disease.
There isn't a known cure yet and the fish is usually euthanized. Cleaning out the tank would be a good idea so it doesn't spread.
But we don't know it's that for sure yet! It could be an internal infection. I just wanted you to be aware of NTD since it requires quick action to prevent it from spreading.
It may easily be an internal infection...I would try Maracyn-Two first. If he doesn't show improvement maybe try Maracyn.
It's also possible he's just bloated...perhaps from over-eating or eating flakes not soaked in water. If that's the case then just fasting him should do the trick.
