Hmm, advice welcome on this as I am on my first hatch (day 15).
I first candled on day 7. Then again on day 9 and a few more times between then and now (already opening to add water). Have not candled today.
One reason I have candled is it is too cool to see them developing
Another is I think my darker eggs are not developing and trying see if anything happens in them OR to check to prevent exploding eggs.
The 12 lighter ones are all alive and doing great.
The 12 darker ones (welsummer and marans) 10 look possibly clear (uniform light) and 2 look dark but have uneven edges to the air bubble. Have since first candling. The maran eggs are so dark it is really hard to see. Never saw veining for sure in any of those. Anyway, that's why I've been candling, trying to see, etc. (yes, I did go buy a strong light).
I was told that if they are not jossled around and do not get cold (less than 10-15 minutes of open incubator) that candling was ok; that momma hen leaves the nest for brief periods of time up to day 18. I always wash my hands first, am very gentle, keep same position for egg as in incubator, etc.
So, apparently the advice differs on this? some say it is ok to candle once a day in this period, (til day 18) some say don't touch at all?
Thanks for your thoughts