Red patch on one Barred Rock

We have 4 older birds in our flock. They're 13 months old. 2 barred, 1 RIR, 1 buff orp.

Just added 1 silver laced Wyandotte and 1 australorp, both little chicks mid Feb. We just got them first into a mini coop next to the big coop a few weeks ago when the weather got nice. They just started co-mingling together in the big coop on the last week or so.

About the time we took the 2 littles outside, 2 things happened. 1 - buff went broody. 2 - the bigs were getting used to the littles and I noticed both RIR and the one Barred Rock had patches below their vent missing feathers. I did searches and thought maybe I had feather pickers with the pecking order, or broody buff pecking. RIR seems to be boss, the buff fancies herself 2nd boss and the 2 BR have never had an issue before. No evidence of lice or mites. On recommendation of some threads I deep cleaned coop, changed bedding, added food grade DE and applied blu kote to the BR several times in the past week. eating and drinking fine.



Here is today's comparison pic. The one BR, now called fluffbutt since she still has floof, and my red patch BR.

Thoughts? Do I need a vet? Try something else? Or apply blu kote more often?