Not sure how much room you have left in your stand, but you could plumb the 2.5 into the sump exactly the way RC said, place a light on it, and have yourself a great frag tank! Also, you could attach suction cups to it and place it inside your display as a frag tray. It might be too big for that, but it's a thought. I had some leftover plexi, so I built a box out of it and use suction cups to hang it in my display when I need to mount a new frag that needs protection or tranquility. I agree that you shouldn't let that tank go to waste but sadly it's too small for a QT. If all else fails, go buy a Beta.