M.H.
I don't know anything about that aquarium (and don't even live near Chicago), but thought I would offer an alternative. Have you looked at what it costs to become a member (if you live close enough)? Our zoo that's about 1.5 hours away costs about $10 a visit, but a family membership is only $59 a year. We go twice and it is completely paid off! Have fun!
P.S. Just looked up the cost...it is $145 a year for a family and it will cost you about $90 if you buy 2 adult and 2 kid passes. I figure in 2 visits you have paid it off, and now you could go more frequently!