Within 3 weeks, I have my NGT to take shrimp, krill, smelt, silversides, massivore delite, aro food stix and of course frozen bloodworms.
My recipe ? We all know they love bloodworms, what I have done is soaked all the food that i want to try in bloodworms while it's thawing in the fridge. I did this with pellets, smelt, krill and market shrimp. Be consistent, be patient and you can get them to eat anything.
Doing this in a QT helps as well as they won;t have to compete with other fish while investigating new food of interest.
You should've QT all fish to begin with for minimum 3-4 weeks. i usually QT mine until it eats my food eagerly, which is 3-4 weeks.
stan