Duck Duckgg day 27 humidity help

[Keely Noodle]

Worrying a little bit about the humidity in my mini incubator, I've managed to keep it at around 65% the whole time but in the morning it will suddenly be really low, like 30%! Despite being about 70% before I go to bed. So in the morning I'll take off the lid and fill up the little dish with enough water and it'll get back to around 65% for the whole day.
I've only got 1 Indian runner duck egg and it's been moving about but haven't seen any cracks yet so should I be worried?