I noticed that a couple of the pellets I tried to feed him sank to the little bridge in his tank. I looked later that night to get them out and they were gone. I let one pellet sink this morning, onto the bridge so it was easy for Artemis to find and it was gone when I came back from classes. I just did the same with another one and I actually saw him eat it this time. He ate it then spit it out then did this a couple times until most of it was eaten.
Maybe the pellets are too big for him? I'm going to try to find some smaller ones when I go next week, but at least he's eating something.