Some times they do not eat. I have a Heckel that is about 12 months old. I seldom see it eat and I have never seen it poop. Yet it is still alive. If it does take in food it usually spits it out. Where any other fish in the tank tend to scrap with one another this one is left alone. It bothers no one and no one bothers it. It also has no color at all except for black vertical stripes and grey body. A discus can live for 2 or 3 weeks without food. So maybe let it be for a week and try different foods. The one I mention does not eat freeze dry anything but will eat some pellets but it takes the fish sometimes 3 times at trying to snatch the pellet into its mouth. If it misses on the third try it will give up and wait for another something to float by. If he gets it on that try he will usually spit it out anyway.