All spoiled and unfertilised eggs should be removed to avoid spoiling of the whole clutch. This should be done the day after fertilisation; clutches should also be monitored to catch and remove spoiled eggs throughout development (daily or every 2 days).
Unfertilised and spoiled eggs can be identified visually, either by eye or using a microscope. Unfertilised eggs will appear unusually large and 'empty', without oil spots or with many tiny oil spots distributed around the egg. Eggs with opaque white or brown spots (or underdeveloped eggs, which are small, solid white) are spoiled and will not develop. 'Burst' eggs with damaged shells will also not develop. Spoiled eggs will often soak up more blue dye from the embryo medium, which makes them easier to identify.
To remove spoiled or unfertilised eggs that are stuck to healthy eggs, the 'crocodile roll' method can be used: with fine dissection tweezers, grasp the spoiled egg as close as possible to the part stuck to the healthy egg, then twist tweezers around to pull the spoiled egg free.