I keep as much water as possible - I want to keep all the nutrients, ph, alk etc as stable as possible. Don't use this as a free opportunity to do a huge water change if possible.
I always replace sand if I'm using it (I rinse super well with a hose in a bucket) - I keep a gallon or so of the old sand and dump in the new tank.
Keep all your rocks, if you have temp probes / heaters, etc etc or whatever - I re-use them without rinsing them. Don't use this as a free opportunity to acid wash all your pumps etc
Basically - I do what I can to keep as much of the old stuff as possible - doing so has made me never able to measure Ammonia or Nitrite after any tank upgrade / swap.
I always replace sand if I'm using it (I rinse super well with a hose in a bucket) - I keep a gallon or so of the old sand and dump in the new tank.
Keep all your rocks, if you have temp probes / heaters, etc etc or whatever - I re-use them without rinsing them. Don't use this as a free opportunity to acid wash all your pumps etc
Basically - I do what I can to keep as much of the old stuff as possible - doing so has made me never able to measure Ammonia or Nitrite after any tank upgrade / swap.
