Crush a few cloves of garlic and soak flake or other food in the juice......the garlic entices them and they may eat it. There are a few garlic additives out there you can get at the local lfs to soak the food in but they are just the same thing.....some food has garlic already in it........I think it is a case of trial and error. What seems to be your problem, what kind of fish, type of tank and other situational issues......maybe there is something else going on