the best way to do it from what I've learned in experience and from Gabe is to go with 100% new sand, and keep at least 50% of your old water, as long as salinity of new water matches your fine. I just transferred my tank not to long ago without disturbing sand in tank I purchased and still got a pretty good cycle. last year I tried keeping about half my sand and the cycle was horrible lost a lot pods and other verts in 48hours. your old sand is holding a lot of gunk and as soon as it disturbed its all released.