Which foods is he taking and spitting out?
Sounds like he holds it just long enough to taste it.I would not give it anything else right now and continue dropping the raw market shrimp.Hopefully it will start eating the shrimp soon before it gets too thin.
so what i did for my NTT to start eating was used some long tweezers grabbed a silver side and wiggled it in the tank. that worked for me. now they eat silver side off the bottom.
do u have any other fish in the tank? I have found that food competition really helps fish adjust to you and new foods.