I take it the collare is an aggressive feeder? I have the same issue with my ulietensis. My yln and Aus cbb both are fairly deliberate eaters except with live blackworms, forcing me to feed heavily so they get enough. No matter what I do, the ulietensis gets the most food, has grown the most, and is getting thick. I have tried feeding in separate parts of the tank, but the more aggressive feeders (ulietensis and saddleback) know to go where the other fish are feeding and hog the food, and then go back to where I started feeding them and clean up. The best option is to wait until the yln and cbb are down-current of where I feed and put the food in a bit at a time to make sure they get enough. Survival of the fittest, I guess.