Well, 2/3 of the the tank water came out of my 20g which was cycled when I dismantled it yesterday. Figured adding 1/3 new water would be like doing a water change?
Unfortunately taking water from a cycled tank and putting in a new tank doesn't make the new tank "cycled". Cycled implies that the tank (filter media, gravel, stones, wood, etc) contains enough beneficial bacteria to break down waste from the fish.
So if you were to move some filter media from your cycled tank, that would help the new tank cycle faster.
As others mentioned, keep an eye on your water parameters as you will probably need some water changes in the near future.