Stereo, although I'm not sure what concentration is safe, tea tree oil is toxic to chickens (and to cats and dogs)-I expect if its marketed as bedding its fine but just fyi. if tea tree oil was safe to use against red mite, we'd all be using it (as an aside, I do work with sheep scab mite and red mite-essential oils do kill them but neat, essential oils aint that nice to everything else. on US forums people have tried tea tree oil and caused neuro problems in their chooks).