When she took the chicks out into the coop, we took the three that did not hatch and there were mites on the eggs.
If the wood ash does not work or if you need immediate results a tiny tiny drop of frontline should do the trick. I used 5 drops on my full size hens as a prevention method. Mainly because I could not find a good way to have all of the natural options in a small breeding pen. We have the food, the calcium, the nest box, and the water, I just could not add any more to the pen. The frontline was recommended on the HRIR thread.