Why is one of my discus not feeding with the other discus?

Question

When its feeding time, 4 of my discus go together as a group and eat the shrimp meal I put in. But one stays behind hiding behind the driftwood. Occasionally he comes with them to feed but most of the time he doesnt. When I first got them a month ago, he always came out with them, but recently he's been separating himself. Just today he was feeding on my pleco's wafer on the opposite side of my other discus eating the shrimp meal. Is this normal behavior or should I be worried?

Answer 1

he must got hurt by a fight with one of the others and lost and now is frightened to come out and may still be hurt

Answer 2

The most likely reason is that he is dealing with internal parasites.  Is it also darkening in color, and possibly passing stringy, white f***s?  I would strongly suggest treating the whole tank and soaking the fishes' food with metronidazole (Metronidazole, Flagyl, Hexamit) or kanamycin (Kanaplex).  Remove the activated carbon from the filter during treatment, and watch the other fish for similar symptoms.  Metronidazole IS safe for your nitrifying bacteria, as it targets anaerobic bacteria and parasites, and will not harm any live plants.