Clean the incubator with soap and water and then disinfect with bleach. Make sure you're washing your hands before you touch the eggs and disinfect your flashlight/candler, too. Calibrate your thermometers, don't trust what the incubator says. They're either being infiltrated by bacteria or your incubator is spiking temperatures and killing them. Consider sanitizing the eggs before they go in, too. I use 50% original gold Listerine and water, considerably warmer than the eggs but not over 100 degrees. Dip and let dry, make sure you make fresh if the water gets cool before you're done dipping.