Yeah, one week isn't very long. Give em' some more time. If it were me, and I wanted some larger BG, I would feed something they could eat....are they spitting it out because it's too big, or because they're not used to feeding? I've seen BG reject pellets because they were too hard, and the fish weren't accustomed to them. For BG, I would aim for a pellet the approx. sixe of the fish's eye, or a tad smaller.
Also, you might try hydrating (softening) the feed and see how that works.

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.