Before and After: Electrical Panel (and an 80 gallon surprise in the wall)

We've been making big progress on our remodel, although I've been struggling to keep up with recording it while my belly grows and my energy wanes with my third trimester of pregnancy. The basement electrical rough in is complete, as well as a much-needed overhaul of our electrical panel. I present to you the "before" horror which awaited us behind the wall: