Yeah, I gotta say that either a divider or another tank are looking like your only options at the moment. A temporary tank like the stock tank suggested above would work as well, but somehow I seriously doubt it would be very temporary given the particular fish you have.
Look at it this way: it's always fun setting up a new tank! --- Man, I wish I could get my wife to buy this line...
The only other thing I can think of is to move the oscar back into the 75, move everything that he'd eat out either into the 125 or the 55, then put the CAEs into the 125. That'll depend on how big the oscar is of course, and how many others he can get along with, otherwise you'll be stuffing too much into the 55 again.
Look at it this way: it's always fun setting up a new tank! --- Man, I wish I could get my wife to buy this line...
The only other thing I can think of is to move the oscar back into the 75, move everything that he'd eat out either into the 125 or the 55, then put the CAEs into the 125. That'll depend on how big the oscar is of course, and how many others he can get along with, otherwise you'll be stuffing too much into the 55 again.