Not sure if sick but need opinion

I have a 75G Discus tank with currently 5 discus. My smallest one which Ive had the longest ( about 5 months) has always had a big appetite, though he hasn't grown much and is still under 3". My other 4 are 3.5"-4.5".
I got back from a 2 day trip recently and half my discus had ich. Apparently from a pleco I had purchased just before I left.
Long story short, I took out the pleco and treated the fish by raising the temp to 87 and it cleared up within a week.
Problem is while my smallest discus appears healthy and normal, he isnt as keen as eating anything thats thrown at him. He will eat freeze dried blackworms out of my hand but immediately spits it out. 9/10 things he eats, he will chew it and immediately spit it back out. I still notice he poops, dark little round pieces. I've tried soaking the food in garlic guard but to no change. Not sure what else to do but my concern is growing.

Tank is 75G
2 Penguin Emperor 400's
Temp 84-85
Ph 7.6
Ammonia 0
Nitrite 0
Nitrate 10ppm

50% water changes weekly as well as an additional 10 gallons every other day during spot cleaning.Attachment 117937Attachment 117938

very nice tank. love the driftwood scape.

Try raising the temperature to 93 F for a week to help it's appetite and metabolism.