I feed my Duncan, Tracky and Ricordia frozen brine shrimp about twice or three times a week.
I found with some mushrooms that they can be temperamental about eating. Also, some that I was never able to feed would all of a sudden start to feed. If the mushroom or Ricordia is "sticky", i.e. food sticks to eat, then it is ready to eat (so you have to stop the current and guar it while it slowly eats).