I would definitely add another feeder and water station. Fill the feeders and let them have access to food all day.
To be honest, one of your problems could be overcrowding. Can you add some perches outside where they have places to get away from each other a bit or a couple bales of hay to...
Do you have multiple feed and water stations?
If not I would at least one of each. It's possible the lowest ones in pecking order are being kept away from the food and water.
Are you still having a problem with piling?
How big is the run?
An all flock type feed usually has around 20%protein.
Corn is not going to "bulk them up". How much treats are included in their daily diet (this includes everything besides poultry feed)?
Continue the Corid.
How old? Around 8-9wks? Parasites could be a possibility, but that's fairly young for...