Its the absolute most frustrating thing I have yet to come across in fishkeeping. Moving them to the 75 didn't help either, now there is more open space for the littler one to swim around and not find food in.
Everyday I drop in a few HBH supersoft for them and the little one swims so close, and I get so anxious that I am literally talking outloud trying to cheer him on like, "Oh get it get it get it! You passed it up go back! No not under the driftwood. Oh well, here comes the big one to eat them all anyway."
I end up feeding that bichir probably 4 times a day just trying to get him to find the food and then one day I saw him chewing on something at the top of the tank and he had snatched a hikari gold pellet out of the current of my powerhead. Unbelievable. I now know if he can't get the food its just because its not moving fast enough.