i went through this same problem just 1-2 months ago. i had (2) 1 inch pbass that were only eating guppies; at about 1 1/2 inches i starved them for 3 days then started with frozen bloodworms, after about 1-2 wks of slowly eating the bloods they all the sudden started attacking the cube; now i've switched them to frozen market shrimp. they are now about 3 inches and in a few weeks im going to start them on pellets.