I bought 3 mille fluer chicks for my friend. The were 5 weeks old when I got them, now they are 6 weeks. One did not thrive and died yesterday. Now one of the others is very lethargic and declining. There is no nasty poop, no breathing problems and no other real symptoms. They just aren't "right". Any advice and treatements would be greatly appreciated. They have dry bedding, medicated chick starter, plenty of water and heat.