Please don't beat yourself up about what you didn't know or realize. You cam here looking for help and I'm sure you will do your very best going forward! We all start our learning adventure somewhere and now you're well on your well on your way to helping your flock have their very best life possible.. to the best of YOUR ability.. and hopefully also be able to share your collected experience and knowledge to help others as well!
DE is completely ineffective at my location due to high humidity. Also extremely drying to already angry skin.
I know they no longer use carbaryl in the US, brand name Sevin, would be effective. It's always interesting for me to see how things work in other countries and if we get a good known method down for you I will try to bookmark it for reference.
I know one of local peeps.. bathes her birds in a solution of dish soap and vinegar, she swears works but I have not personally tried.. Which.. dish soap helps break the surface of water.. and vinegar when I use it to rinse my strawberries dries out the leaves immensely.. plus acidity helps breaks down calcium, which I am unsure if it has any relevance to helping defeat any egg structure that's there??
Walmart here also sells a product called Poultry protector that MIGHT work..
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Good job, being diligent to find out what's going on and following through! Keep up the good efforts!