Tips to make my discut eat pellets/flake food?

I tried to feed my discus pellets today. At first, they didn't look interested, but when I turned on the filter to make the food spinning around, one of my discus got interested and ate a bit of it. Not even a second, that little guy spitted out all of that food. I also tried to make them eat flake food, this tome they completely ignored it, the flake food sinked down... Any tips to get my discus to eat pellets? Also, what discus pellet brand is recommended? Is TetraBits okay?