First time hatching duck eggs question

[Doulos]

So, it's day 14 and all the eggs look healthy except one. When I candled, I noticed one egg had a cracked shell, and while the other eggs are red, this one is much darker (almost black) and I can't really see if anything is alive. There seems to be a small air pocket developing. It has definitely changed since day 7. I would post a picture, but I can't get my phone to take good quality pics. I'm just wondering if that egg just has a bunch of bacteria inside. Should I remove the egg or let it stay? My main concern is contaminating the other eggs.