It sounds like they're getting diarrhea from foods that have a high liquid or sugar content.
Layer pellets should really be the bulk of their diet. They might even be missing something important because they're getting junk food every day instead of food that's been formulated for chickens...
I give mine chopped tomatoes and mostly vegetables and fruit. We buy the long, skinny lettuce (I think romaine?) and they get the weird nubs at the end and eat them til there's nothing, along with cucumber skins/cucumbers, squash, cantaloupe & watermelon rinds, grapes, bananas, cooked eggs...