Good luck. I've given up on them. Seem to starve. May need to stick some meaty food under him from time to time. I don't know, but my guess is that if he were finding food in the sand, he wouldn't be on the glass.
Once you see his body get appear as sand is sticking to it, he's beginning to have serious problems. I use nassarius vibex snails for my sand stirring now. Best thing since sliced bread for me.