Unless you want to throw that tank into start over mode, slow is the way to go. Get a 10g petco special or a bucket from HD and cycle the new rocks, live or not. Start with a rinse in regular rodi water, then into some salt water, then over time you do your water change from the biocube into that QT tank as it's water change, eventually it has basically the same water. The shock value moving to the display tank eventually is minimalized a bunch. not perfect but it gives you the change to avoid spikes, avoid introducing bad guys if you find them in that QT, and should create a higher chance of success since any die off should happen in the QT process. the above is my opinion and not based on science just my years of experience and painful lessons learned.
