good that he's taking some krill, keep him eating that but if you don't have feeder rosies then go with guppies...they won't start rotting if the gar misses them, and if you keep the tank well stocked for a while he will fatten up sooner and hopefully not end up with development problems. the krill alone even once or twice a day will not catch the fish up to appropriate growth.
also, keeping the young gar with cichlids is not the best idea as they can harass the fish (even at night when you can't observe it) and also compete for food. they will also counteract the feeder method as they will be more likely to catch the feeders first. if your priority is to get the gar back into good health, i would separate the cichlids, keep feeding krill, and provide a steady supply of feeder guppies at least for the next week or two. good luck--
--solomon