When turning eggs in an incubator by hand, it is easy to detect most cracks and seeping or oozing eggs, and to smell odors of a suspected rotting egg.  Remove and dispose of those eggs immediatly. 

Candling eggs: When an automatic turner is used, spotting problems might be less noticible. You might choose to candle.  I hesitate to tell you to pitch eggs that appear to be clear from days 10-12. If you candle the eggs at 12-14 days, you should be able to tell if the egg is fertile. If you not 100% sure, candle again in a few days, to be absolutely positive before deciding to discard an egg that might very well  be fertile.  If you have a ratio of 6:1 hens to cock or better, under proper conditions (if the hens were fed properly and the eggs were stored and handled correctly from start to finish)  you can usually count on a 90% hatch.  Keep this in mind when candling.

There are several different kinds of egg candlers available to purchase, some lot less expensive than others.  Standing in a pitch dark closet while looking through an egg held against a strong mag light is a quick alternative. 

A fresh egg appears clear with only a small air cell. After 12 days of incubation, an infertile egg has an enlarged air cell, and the yolk causes an obvious dark area in the egg.   After 12 days of incubation you should be able to see visible blood veins in a fertile egg.  Later, you might even see a moving embryo.  Do not be surprised if you candle and never notice anything more than a dark shadow that later hatches into a  healthy, beautiful little keet.

The eggs in the following pictures are chicken eggs.  Chicks develop and hatch in 21 days,  whereas keets take 26-28 days.

Humidity is a constant 60%.  Raise to 80% the last 3 days of incubation, which would be on day 23 for guinea eggs. In most home incubators for hobbyists, this is accomplished by adding water to the second water trough in the bottom of the incubator.  Please read the instructions that came with your particular incubator.