Are you still trying the tetra crisps? You're not giving them enough of a chance. WE know it's food, they're more picky. Also don't get so worked up, they can go longer than 5 days without food.
Stick with frozen brine shrimp and bloodworm twice a week and feed soaked flake on other days. It WILL start eating it, mine took over a week.
Also like I suggested before, try sinking tablets. All fish can feed off them, not just bottom feeders. And I mean all-round food tablets, not algae wafers.