This morning when I checked on my chicks, one looked a little lethargic and was closing its eyes and seemed to be breathing a little hard. I watched them for a while and noticed the chick had whitish poop. I had to go out for the day and when I came home it was laying down and breathing hard. I took the chicks out to see if it would perk up being outside, but it just seemed to lay there as the other chicks walked over and even pecked at him so I decided to move him inside into its own box. Within two hours it was dead. I have cleaned the brooder well and sprayed it down with vinegar. The other chicks seem to be doing well, but not as perky as before. I am new to all this. Does anyone have any ideas what has happened and if there's anything I can do to prevent this from happening to another chick. I have two chicks now that are almost four weeks, but in a couple more weeks I'll be getting twenty more.