Does anyone remember the thread about a square of aluminum foil over a nest box that BYC started?
I think it was an April Fool's day joke but I never looked too much at it.
Apparently it was supposed to help hens lay better.
Temp and humidity are the same for duck eggs.
They do take 28 days as opposed to the 21 days chicken eggs take.
You can set the chicken eggs in there too. (I do it all the time)
I like your idea of using an aquarium as a brooder.
I have one that is mainly a "dust collector" right now, but now that I've seen your post, it has a purpose once again!