It's been said on here before to feed fish pellets that are roughly the size of their eyes. GFC has a vairety of pellet sizes in it, the largest being roughly 1/4". AquaMax grower 500 has basically the same pellet size that you are feeding now.

http://aquamax.purinamills.com/aquamaxproductlist.pdf

www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).