Weeks ago, I had a mite problem on my flock. I bought Permectin to kill them, and it worked like a charm. I knew I would have to reapply in a week, so when I got all geared up, I checked them to see if they still had mites. They didn't, so I left it because I don't like chemicals anyway. Now, it looks like they have had a relapse. How do I keep this from happening? Thanks!