I have 2 crabs and had some similar problems at first. What I found
were 2 things.

1. They were less likely to eat them if there was other stuff to eat in
the tank to eat first.

2. It took them, and the plico, a while to learn what this strange,
disk thing I was putting in the tank was.

So I figure it just takes time. Also, they don't seem to like them
unless there is nothing else in the tank for them to eat. Because of
this I only give them little peices every couple of days. Good luck.

Travis