I made an incubator out of an old mini fridge, programmable thermostat, and light bulb. There is a small pan of water for humidity. The eggs seem to start out fine, but about the last week everything dies in the shell. I have only had one chick hatch out of 3 tries with 2-4 dozen eggs at each try. There is a small vent hole to prevent overheating. I have hand turned the eggs 2-3 times a day with each run. What am i missing? I have had success with the little styrofoam incubators, so I know eggs are good, along with candling and seeing chicks forming. TIA for ideas/suggestions.