it just depends on your egg chamber/box. If your only using an inch of perlite and have multiple holes in the box for air then your gonna lose what little humidity that you create. I'd just make sure that there is at the very least, 2-3 inches of perlite/water and little to no holes in the tub. For the past two years, I used about 2 1/2 inches and only one hole for the t-stat probe and had 100% hatch rate (I did end up having to add some water to the mix somewhere along the 60 days). So this year I think I'm gonna use more perlite/water....