Mine is a fairly picky eater. LOVES frozen bloodworms, won't touch too much of other stuff.
Feed right after the lights go out, and have as many room lights out as possible, perhaps have a hall light on or something so your eyes have just enough light to see (after they adjust to the dark). put in some frozen bloodworms and see if he'll come out to eat.
I suggest buying or making a moonlight system. I made one with a few LEDs, and don't have it very bright, just enough for me to see what is going on in there when all the roomlights are out.
also, what other fish are in the tank with it? anything that might be harrassing it? how big is the BGK now?
good luck