All of the chicks on their backs would be culls for me. I think the age of the eggs probably contributed to the delayed hatch as well, but sounds like this batch of eggs had several things going against it. I really think your improved eggs and lower humidity are going to yield good results this time.Fertility rate was a big issue this time. 67.5% in the Janoel, and 65% in the Brinsea. I expect there's some correlation between that and the nutrition issues. 33 hatches, 2 post-hatch deaths, 8 struggling chicks (including one that is still in the bator, I was doing eggtopsies and mistakenly thought it was dead and when I cracked the egg, it moved a lot!) Assuming all the strugglers die (which I expect most will), then this hatch is a 47% success rate.
Its hard to make a comparison between the Janoel and the Brinsea. Clears were roughly equal in both. 7 pre-hatch deaths in the Brinsea, 13 in the Janoel...but I'd have to see that through several more settings to say its a bator thing. Only 5 of the bator deaths were late deaths, but of course that number could go as high as 13 if the strugglers all die.
Resetting the bators later today.
What is your display temp set at on the Brinsea? I never saw if you found an average temp with the Spot Check. Bumping up to 100.0 stopped my delayed hatches