Hmmm..
Well depending on the type of Barbs, sometimes they will attempt to 'graze' on rays or even peck at them.. I know Tiger Barbs can be nippy at time, especially if they aren't in a large enough school..
The strip lights might entail it is a fairly small tank.. What size is the actual tank? Anything that can stress the ray, such as lack of turning space, could cause him to stop eating.
I would keep attempting to feed those chopped worms!
Try to peek at his underside if you can.. if its pink or reddish, you could have a few problems.. Such as an irritable sand substrate or ammonia in the tank, not breaking down fast enough..
Also, I dont know much about the black titanium moon sand, but hopefully it's ray safe.. and make sure the white sand you mixed in isn't silica based.. Make sure that the moon sand isn't calcium based like aragonite, or it will mess with your water chemistry..