Incubators that use aquarium heaters are for eggs that require high humidity, such as reptile eggs. Reptile eggs rapidly dry out if the humidity is too low. The aquarium heater provides warmth for the developing embryos, and the water that evaporates keeps the air humidity up. Using this method, you can successfully hatch baby reptiles.
Pour water into the aquarium, cooler or large plastic container until it has about two inches of water at the bottom.
Set the thermostat on your aquarium heater for the correct temperature. The temperature will depend on the type of eggs you are incubating. Place the heater in the bottom of the container so it is entirely submerged.
Fill your smaller containers about halfway with egg medium. This can be peat moss, vermiculite, or sand, depending on the species.
Poke holes in the tops of the egg containers with a pair of scissors. This is for air exchange.
Add water to the egg medium, enough so that it is moist, but not so wet that water squeezes out if you squeeze it in your hand.
Make depressions in the medium with your fingers, and sit the eggs in the depressions. The medium should come approximately halfway up the egg. Place a thermometer inside one of the egg containers, and put the lids on the containers.
Tilt the egg containers a little, so condensation doesn't drip down on the eggs inside.
Check the eggs for signs of mould after a few days. If you see mould on any of the eggs, it is a sign they are infertile. Mouldy eggs should be removed using a spoon.
If the water in the bottom of the cooler is deeper than your egg containers, you can set them on a brick or piece of styrofoam. Check the water level in the large container every other day, adding more water as necessary.
Make sure you place the eggs in the medium so that the side that is up is the same side that was up when they were laid. Otherwise the embryo will die.