Hi,
A couple of points from me ...
Mite powder is more of a repellant (unless you use "total Mite Kill" - which shouldnt be applied direct to the birds)
To treat lice you need a louse powder applied to the bedding / nest areas etc, then mite powder in the birds them selves (not Mite Kill). - this will encourage the lice to leave the birds, and the louse powder will kill them.
Using a medicine intended for humans (Diacalm) has a couple of problems 1) What other problem could you be masking ? ie why has the bird got the runs? 2) what effect does this have on the eggs? is there a withdrawl period involved? etc.
Flubanvet.... well as I have tried to point out in the past, very may well have a withdrawl period for commercial use, and if you sell your eggs at the gate or to friends then you are a commercial producer.
Thanks