How many people candle their eggs?
The science teacher in me must candle at 7, 14, & 18 days. We number each egg & write specific observations in our chart. My average hatch rates fall between 80-90% for local eggs & 60% for shipped eggs. I just can't explain my last hatch of only 20% in the shipped eggs. Ten looked great on day 18 but only 3 hatched. The other 7 never even pipped the shell.
Note: I used to leave all the eggs in the incubator until the end when we do the egg-topsies. I discovered that an egg can literally explode due to bacterial growth. Very messy stink on day 20 while 3 chicks were pipping. I believe they must have bumped the rotten egg. Because I had to do a rapid incubator cleaning at such a critical time, I only got a 45% hatch. (Many died mid hatch.) Happy to get any chicks after that mess. Now I always remove blood rings, clears, & definite quitters.