I'm so sorry none of the other eggs hatched.Yes, what you're saying describes well what we now believe to be the core of the problem. We were just first time duck parents and had no idea what kind of realistic range of parameters to expect / provide, so we went by the book and lost at least 8 ducklings because of it.
Just now we've decided to open one of the 8 nothing-going-on eggs and, as we suspected, found a fully developed duckling inside a very dry membrane - despite having started high humidity in the incubator a day before the instructions said so, ie. Day 25 instead of Day 26. We should have done it even earlier.
Basically we had a Jack Sparrow episode ("the rules are... more like guidelines"). It was not a happy moment to see the developed but dead ducklings. But we can do better in the next round. We're ready for a new batch starting tomorrow.
The two rascals that did make it are growing and crapping heroically. Yes I did read everywhere that ducklings are messy but duuuude. We are handling it though. So far we've used puppy pads, tomorrow when the wind is supposed to ease we're planning a sports day in nature (nice clover area, 4 x 4 x 1 ft playing pen, 3/4 covered), we'll check how their legs have improved and then we'll probably switch them to straw. We've just brought in one m3 of nice barley straw.
How do you handle humidity in the final stage (before hatching) to ensure the shells will be easy enough to break through and the membrane does not dry out? At what day do you usually start increasing humidity to cover the widest range of situations, and to what degree?