+1
Yes do as Homer said. That's how I migrated my fish from a 125 gallon to my 250 gallons. Transferred biomedia and water to the other tank with some test fish. Evil me, I even added my most hated carpintis first and if I see him getting dizzy, I return him back. I did this after trying on feeder goldfish first, though, and after they all stopped dying. After some time that I found him (the carpintis) establishing a territory already, it's time to add all my other fish 2 at a time per 6hours. Worked like a charm.