I had this problem with 2 types of fish..
I had this first with my frontosas that I got. They would not eat. They didn't eat for I would say 3 weeks. The woman we got them from was feeding them some african cichlid pellet, which she included... then someone told me on here that its best to keep them hungry so that they do eat.
They eat Hikari Gold cichlid pellets now. And they eat for 3 days, and then they don't eat for a day, and then they eat again... it's a cycle.
Now, for my Jacks.. NOTHING i put in the tank made them eat... I honestly didn't see them eat for months, although i knew they were eating because the food would be gone in the morning.
One day I got a Jag cichlid, and he came with some dried krill, so I moistened it and threw it in. Holy Moly! It was like bass coming up for bugs.
So now I moisten the pellets in the shrimp juice, and everyone eats just fine.