Good for you! Yeah, seems like everything Tetra makes is junk, including the food! Mine love frozen bloodworms, Emerald Entrée (brine shrimp w/spirulina), regular brine shrimp, krill and Mysis shrimp. I rotate them all, giving pellets and flakes every other day. That way they get a big variety. Also, veggies and fruits cut in teeny pieces are also good for Rainbows. The shrimp pellets are a nice treat too, and you can crush them or soak them so they are easier to eat. I must have over a dozen foods for my fish!
So glad to hear he's eating! My Rainbows also frequently "barf." They are pigs, and try to get pieces that are too big into their mouths. One time one of my girls had a shrimp pellet in her mouth, and had her mouth wide open for the longest time (well, it was probably only 10 minutes, but seemed longer) and finally the shrimp pellet came bursting out. So now I crush or soak them.