he probably does have internal parasites.
A likly indication that you can see is sometime they have 'stringy, white poop' trailing from the anus.
that is also a small FA.
what are you feeding him now?
The other thing is, flames do much much much better in an established tank, as they pick on the rocks ALL day long for things. so they need lots of stuff on the rocks to pick at and eat
Is his mouth OK? Meaning does he have any white area around it? Just make sure the mouth looks fine.
Also did you buy him really skinny?
make sure to get him some 'angel' food to help him along, some foods contain things like sponges or sponge parts that really help them.
Pellets, there is an angel variety that should help fatten him up some.
You should de worm him to, especially if he is wild caught. Prazi-pro or another dewormer is a good place to start. IF you can get the kind that goes into the food that IMO is better as he actually is eating it, but either way (food or a bath) should help him.
