I would remove the DE since it does nothing in the food to prevent worms, becoming worthless when wet inside the body, and it can be dangerous to breathe. A respiratory disease called infectious bronchitis can cause snicking or sneezing, and it can spread throughout the flock over several weeks, lasting around a month in each sick chicken. It usually does not cause the wheezing, gunky swollen eyes that some respiratory diseases cause, and is the most common respiratory disease. Usually adult chickens tolerate it well without much trouble, although it can cause a decrease in laying. Young chicks and juveniles may become more ill or die. IB is caused by a virus, and antibiotics will not help. It can be complicated by bacterial secondary infections if symptoms appear worse, and an antibiotic such as injectable Tylan 50 might then help.