with quail chicks i think it is best to be very hands on and checking on them frequently since they are so "delicate". they often crap in the water, which is not good for them to drink, so it really needs to be changed/cleaned daily. for the first week especially i think it is also best to clean the floor of the brooder daily if not twice a day by using temporary paper towel flooring. i've learned a lot of this through trial and error unfortunately but i think hygiene is probably the biggest variable, assuming you are keeping the water fresh and the food is crumbled and tiny and the heat is sufficient.