I feed my chickens ff. I make it up in a 5 gallon bucket, usually have 2 buckets going as I have around 50 chickens. I use eual amounts of water and feed and stir it a few times a day, I spend a lot of time out around the coop so it's no big deal for e most of the time. Mine is usually bubbling around 3 days, and has a smell to it but I do not think I'd call it sour smelling. Once it is getting close to half empty I make my other bucket. I take a big scoop of the ff I already have and then equal parts water and feed for the rest of the bucket and stir each day until the other used up and just go back and forth that way. Its really very simple one you get it going. I dont reuse the water, because my feed sucks up all the water, and I use single bucket method. But there are alot of different ways of doing it. I have never adding anything other then the food and water on mine.
I wish I could help you with the mites, but I have not yet dealt with that. I hope that someone comes along with some good advice that works fast to cure that up for you. Good luck with the chickens.