hey mate. all above suggestions are good. if u want little fish to have a chance, try feeding them at night when the big fish are sleeping. also maybe try giving big fish a big piece of shrimp so they stuff their mouth and go off and chew it in a corner so the little fish can have a turn lol.
also, I have a small gt in with mybig fish, and have recently started feeding it hikari discus bio gold, the gt loves it, and the granules seem to be too small for my big fish to even notice its there. its also 53percent protein so will help ur gt grow faster. good luck! 8)