why are they cracking and rotting?

bad eggs will rot and break in the bator. do u candle them every so often to make sure there good?

 

Are these eggs from your chickens? If so maybe they need an antibiotic of some kind? More calcium?

So far I have only had 1 rotten egg and it did not blow(thank God)! My past hatches have been zero hatch rate. So I took apart my incubator and cleaned with bleach and rinsed, then cleaned it with equal parts vinegar and hydrogen peroxide and I added a little water, and wiped it out. My flashlight for candling was cleaned and I replaced my felt circle that I have covering the lens. I took out my sponges and replaced them with a small mason jar with some aquarium gravel(about2") that was cleaned with the vinegar and peroxide and filled with bottled water(4"). So far my humidity is running a stable 42% and my shipped eggs are doing great!

 

I would suggest you clean, clean, clean, clean, clean that incubator! Sounds like you may have some bacteria in there. and eggs being porous, they are getting humid, sucking in that freshly grown bacteria, and going bad on you. Always candle and sniff those eggs! Toss any that start stinking.

 

There are many good univeristy web sites that help you trouble shoot.

Starting with very good eggs is essential. Hens need to have been fed a good diet for the best success, and this included plenty of calcium for strong eggs. General good health is also required.

Set suitable eggs. Clean uncracked eggs of normal shape. Candle and cull cracked eggs.

Clean incubator, and disinfect between hatchings.

THere is more at the universtiy sites that post trouble shooting info.

Sorry you are having trouble with cracking---you will find the answer!