It’s not unusual for a first clutch to be just one or two eggs. As long as you do not see signs of her straining, like she can’t lay another egg, then I wouldn’t worry about it. Cockatiels really should not be set up for breeding until they are at least 2 years old. If this pair is younger, that can also explain the single egg.
Nutrition is also very important. You mentioned chop, which is fine as a supplement, but it should not make up more than 20% of their diet combined with their other extra foods. The pellets should be 80% of the diet. I know chop is trendy, but produce starts to lose nutrients from the moment they are harvested. There is no way to know how much nutritional value your birds are getting out of produce, even if you grow your own. There are too many factors that can affect the nutritional values. Seeds are important for a cockatiel’s digestive system, because they do eat seeds in the wild. But the seeds in loose mixes are generally not fresh enough to retain their natural nutrients, and any added vitamins are lost when the bird hulls the seed. The best way to offer whole seeds is by feeding our foraging diets. Our Nutri-Berries, Avi-Cakes and Pellet-Berries are formulated the same as a pellet, but they are not ground up. We use fresh, hulled seeds so that the nutritional binder we add can be absorbed. These diets can be fed instead of or along with pellets.
Don’t worry too much about this first single egg clutch. Let them practice, and don’t be disappointed if nothing comes of it. First clutches almost always fail. Once they are done with the egg, or if a chick hatches, once it leaves the box, remove the nest box. The pair should be rested for at least 6 months between each clutch, whether the eggs hatch or not. Cockatiels will breed over and over if you let them, but they are not intended to do this, and letting a hen lay eggs too often can eventually cause her to die from the stress on her system. Hopefully next time she will lay a full clutch. If she continues the single egg clutch, then something is not quite right with her reproductive system. Not all birds will be good breeders.
Thank you for asking Lafeber,