Switching to bigger tank - will I be restarting my cycle?

[SnifflySnail]

I have a 5 gallon cycled tank that I’d really like to upgrade. I was wondering, since the sponge filter I have is meant for up to 20 gallons, could I just transfer everything (including plants, filter, heater, substrate) and the new, larger tank be cycled immediately? Or would adding additional substrate and water crash the cycle?

 

[Littlebudda]

Yes but just add any additional fish slowly so you don’t get a spike

 

[Fishfur]

Even if the filter was a tiny one, if you moved it and the fish it supports to a larger tank it would still support the fish. The extra water would not matter. But add any new fish gradually so the bacteria can catch up with the additional bioload without being overwhelmed.