2 of my chickens were acting lethargic, not eating, and only drinking.
They were unresponsive and would sit still or only stand in place, they died one day apart from each other. I took one to my local vet, she said she wasn't sure what to do and isn't trained in chickens.
One of my other chickens is now lethargic-- won't dig or scratch, won't eat, only drinks water.
Her crop was very full of water,
Runny, white, and highlighter yellow.
Not able to get a picture of set up, but it is an outdoor run on a dirt floor, with a typical feeder and ground waterer for the Corid. I usually have a nipple set up for watering instead of a ground waterer.
I agree with treating for Coccidiosis.By drench dose, do you mean a concentrated dose of Corid, or the mixed dose but just administered directly to the beak?
Since you are going to see the vet, see if she can perform a fecal float checking for worms too.
They are only drinking water and you have one that has a very full crop of water.
What have they been eating? Anything different?
Are these hens laying eggs?
I would re-check crops first thing in the morning to see if they are empty.