teceem: I read all the journal/mission entries and non of them mentioned DLC or even the title of that DLC. (and Citadel alone is unclear because there are a lot of other missions with Citadel in the name).
Well most involve taking a trip to a nonstandard area of the citadel(i.e. not one of the basic floors usually reached via the main lift.), and iirc there was a way to tell which was which(dlc vs standard missions).
That said I hope you're having fun, and if you didn't do it yet i'd do
citadel(the dlc) as follows:
*Maybe minor pseudo spoilers* Once you get the chance to do it, do the main starting bits of it(first few missions at apartment) & anything you can do in the connected areas(barring doing more of the main storyline of that dlc), then leave the apartment area(i.e. go back to the main game) until you do a major/minor main game mission out in the main game, then come back to the apartment area to check for new stuff to do and do a bit more.
Save the
party(in the DLC) for just AFTER helping miranda on one of your other missions.
Hope the above helps :)