Small adult or juvenile not willing to eat

I have had one smaller c. orientalis with four other bigger adults. Those four are breeding and eating healthy for a long time. However, this smaller one has been slowly became weaker. When I first bought him, he still willingly accept food even with hand feeding. It would even go after the food. However, ever since I introduced java moss in the tank, it started hiding a lot. And now a day, it will just swim away if I hand feed it. Therefore, most of the time, it will only take the first bite and then ignore all the food.

I have been mostly feeding frozen bloodworm. As it started rejecting food, I introduced chopped earthworm to help it eat. Although it enjoyed the first meal of that, it continued to reject food on second attempt.

Anyone have any suggestion.