I have 11 four week old chicks in a seperate part of the coop. Since yesterday morning I have discovered 4 slightly bloody stools. I recently switched them from the medicated starter mash to flock raiser crumbles (non-medicated). They have been on the crumbles for about 1 week. Do I need to treat with Corid or can I put them back on the madicated starter feed? Which is better?