One of my hens, a speckled sussex, has lost her appetite and doing a weird thing with her head/neck. Hard to explain, but stretches it out and back again. I went to the coop tonight and felt her crop and felt air in it. Not sure if this is normal. I have felt air in it before when she was acting fine. I went to feed store and purchased Duramycin-10 antibiotic hoping it will help. However, I can't figure out how much powder to put into how much water. The bag has 10g of powder. From reading it, it looks as if I need 400 mg to each gallon per day. I'm not a math wiz nor am I as smart as a fifth grader so how many spoon fulls is 400 mg of powder per gallon?