Oldhen, I wonder if you are feeding a little too much egg is it makes your chicks loose? That is often a sign of excessive protein. It's another reason I use a little Quaker quick oats in my chick mash, cuts protein a bit and adds fiber.
I agree it's important to not leave the eggs sitting around. I start with a yolk or partial yolk, depending on chick number. Then proceed to whole chopped egg. They do go crazy for it!
You might try googling how much hard boiled egg to feed. I came across it recently and it was many more chicks per egg than I'd thought. However, I start chicks on a small amount: maybe just the yolk daily for a dozen chicks.
Eggs are a perfect food, and great for chicks. I do not "treat" but...