I'm currently downgrading from my 180 mixed reef to a 100 tank. I want to now stock more SPS corals. My question is if I'm keeping the rock and some of the coral, how much of the water in the 180 should I transfer over and how much new water should I mix in with it? 50/50?? 25 old/75 new? I've decided to put in new sand and seed it with some sand from the 180. Should I let the new tank run for awhile (a couple of days?) before I put the stuff in? Or can I immediately start moving stuff over? Thanks for the suggestions!