So, Bee, could I pick your brain on my chickie problems as well? I will try to be brief... 
We got our first chickens (24) in late February. Brooding etc. went fine and no troubles until just the last month or so. All were laying wonderfully, and then...
Mites. I was shocked because I thought I was doing everything right. Using DE in the nest boxes under pine chips and deep litter (straw) on the coop floor, feed off the floor, buckets w/ nipple waterers, free ranging almost all day everyday. I'm not sure where the mites could have come from but the environment. I had never heard of wood ashes (will use that from now on!), and the mites had really gotten a foothold on the nesting area in our 8x8 coop before I understood what they were or what was happening. So, per several suggestions, I removed all that bedding that was starting to compost so nicely and scrubbed every nook and cranny of the coop and boxes and perches with soapy bleach water. Everything dried in the fresh air and sunshine, then was painted with a DE slurry to seal possible mite hiding places. The mites were really bad, though the chickens themselves didn't seem to be crawling with them, really. A few had bite marks on combs, but I never found any crawling amongst feathers anywhere. So I've restarted the deep litter (with DE underneath - Grr! Wish i had read this first!) and kept the nest boxes very clean, since I saw the mites trying to re-infest.
Now I see little to no mite action anywhere, and the mite bite marks seem to be disappearing one some, but not others. The BIG problem: They stopped laying. They has started slowing down previous to the me realizing about the mite invasion. Now I have ONE Black Australorp that has been faithfully laying each day, but that is it out of 21 who were laying. I have 10 that out to be coming into lay about now (22 weeks). They all look healthy save for the teeny tiny black dots on their combs. The only other 'symptom' that i have noticed is a few of them have slightly faded combs and wattles. Not bad, mind you, but not as red as they used to be. I would say that they look as if they had dry skin.
Other things of note: We lost one of the young chickens right out under the run fence from what we assume was a coon. They were being locked in the coop while we were away for a funeral and a friend was caring for them for us. Also, a dog/coyote has been lurking around our property. It snatched two of our hens back a couple of months ago. (GRRR!) So they get put in the run and locked in mid-late evening, just an hour or two before they turn in. When we cleaned the coop, we eliminated a very high perch due to nightly squabbling and the fact that it was just above my head. Ew. Too many emergency hair washings from that. Ick. I didn't know if any of these factors could be affecting the lay issues or not, so I thought I would mention them.
BTW, this thread is EXACTLY what i have been looking for!! Your experience and info have been such a wonderful thing to receive! Thank you SO VERY MUCH!
Oh, and so you won't have to ask: Its an 8x8 coop with ample perch space for all birds, 4 nesting boxes inside. There is a 8x20' run on either side of the coop. But mostly they have free run of nearly 2 acres. Mostly grass, but they seem to really prefer the line of honeysuckle trees not far from the coop and just beside the house. Easy access to leftovers tossed out the kitchen door... They are on layer pellets, get a little scratch once or twice a day, and I will start tomorrow with the ACV in the water. Didn't know about that until now, either.
Ick.
