I did a complete change of new gravel, into a completely new tank, and 100% new water. The only thing I put on the new tank from the old one was the filter with the bio-wheel. I tested, and did not have a re-cycle. This may only apply in my unique case though because I was moving to a bigger tank (from 10g to 20g), and I didn't have a big bio load (just two pristella tetras and a ghost shrimp). Also, my bio-wheel is what was holding the most bacteria. If you have a big bio load and don't have a bio-wheel, I would be careful not to cause a re-cycle.