I have perfect, clean-as-a-whistle hatches when I keep my last three days' humidity between 65-70%. Before that, I keep it between 45-50%. If you put it up to 80% those last three days, you will drown the chicks. They also need ventilation, as they are breathing creatures. Some make the mistake of covering all the air holes around the bator while trying to get the humidity too high. Make sure your instruments are reading correctly, too.
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