How to pump up these discus?

[stanlee]

I have some discus in a com which are small eaters, but get this sunken look if u look at them straight from the front.
no hole in the head , but still active and lively but seem to be "choosy" when picking at the food.
i feed them beefhrt, bld worms, tetrabits but still they cannot recover from this sunken look.
they don't seem to be sick (the stools are not white or suspicious), but just cannot get them back to the fatten look.
usually they will start by being bullied in the com and before u know it , they will become like this.

if i separate them, can anyone help in opinion on how to get them back to shape and if possible how long.
i tried tubifex but a bit worried though they seem more increase in appetite.
thnks

[pcsb23]

If you have a scope it would be worth examining a fresh fecal sample, likely that you would see the evidence in there.

My best guess here, given they are eating properly, is that they have some form of worm, most likely a round worm (nematode). Fenbendazole in food (panacur contaiins this) or levimasole in the water.