So you're talking about the 5.25 frame inside the case?
If this is so, I might have a clue what you are talking about

The bottom angle is to tight for the aqua drive?
Do you have to use the lowest 4 slots or can you switch one slot up?
If you use a DVD drive, try to use the upper slots for the aqua drive and put the DVD drive in the lowest slot.
If the bottom angle of the 5.25 frame messes with the aqua drive switching the slots up by one position might be the only chance. Well you could cut out the the bottom of the frame, though :

Wouldn't be the first time cases got mutilated for the sake of water cooling.