The issue I took with the product posted was that it is aromatherapy grade and likey states on the bottle "not for internal use", unlike the oil of oregano that you speak of. Even with that I would only use it in a second waterer as an option for them, not as mosquito control. From what I've gathered, OP will not have the mosquito issue anyway as those small waterers won't stay full enough long enough.Again, don't get me wrong, I love holistic treatments, and use Oil of Oregano all the time. I use oregano all the time for immune boosting, and essential oils often for diffusing. I actually have Oil of Oregano in my first aid kit awaiting the day I ever have to use antibiotics, and plan to try Oil of Oregano first knowing that there are studies showing it can be just as powerful as antibiotics. Overall I love the idea, essential oils just concern me. If you have found a dosage that works for you, thats great! Maybe it wont cause any issues.
There is this thread on BYC that talks about the subject, that would be a good start- https://www.backyardchickens.com/th...dosing-benefits-can-it-be-used-daily.1527452/