My guess on one of your causes of the low hatch is that it sounds like you were opening the bator a lot--candling, and turning your duck egg, etc. EVery time you open the bator, you lose your humidity. It is said you shouldn't open the bator at all, if possible, during the last 3 days of hatch. I didn't know this on my first hatch, and about 3 or 4 hatched, and I opened the bator to take them out, etc, and no more hatched. When I gave up on them, I opened the eggs, and most of them were fully developed, dead chicks. I feel sure it was that I opened the bator and lost my humidity. Just my thoughts. Good Luck!