Can you use the water also? It's hard to say, you might have a "mini" cycle, if any. It also depends on what you are upgrading to and from. I just went from a 30 to a 36 (small upgrade), used my live rock, about four cups of sand from the other tank and 15 gallons of water from the old tank and did not have a cycle. I have always vacuumed my sand during water changes, I would hesitate to use to much sand from your old system if the sand has never been vacuumed. I was also careful not to use any sand that was underneath rocks and never disturbed.