I have two of those gobies and I find you have to aim the food directly at where they are currently residing (mine move around every few days which is a total pain). I find these gobies are rather stupid, they don't recognize food until its practically on top of them, and even then its a crap shoot. I find if I soak the food in garlic it seems to trigger them to come out and get the food. That might work for you as well.
Good luck.
Christy
