I just switched over my 30 gal
to 100 gal
. I did lay down new substrate, used a small amount of old substrate to seed it. Transferred all of my old live rock, corals, etc. Then I used my old tank with remaining sand to cycle my new live rock before putting it into the new tank. All went very well. I did this within the past 6 weeks and have tons of pods
, lots of evidence of good life. I am just now adding the new live rock to the tank.
In a different situation previously, I did do a transfer where I stirred up all of the sand, which created an ammonia bump, but only to 0.5, no nitrites or nitrates due to well-established tank.
Just my experience.