start up

how do you cycle a new aquarium while already having fish in the tank? How to make sure the fish don’t die with the fluctuating of the tank getting established again?

Hi,   I've been keeping tropical fish for about a year. The last 6 months I've had a 10 gallon. I have moved and am upgrading to a 30 gallon. I bought a used-piece-together kit from a local-ish guy. I want to plant it. When placing the tank and stand against the wall, I realized that there is no...