agree with Derek. The bacteria colony is essentially in your filter and soil. The water would only benefit fish that you wish to put from the old tank to the new. When you do the ceramic change, I would still monitor the levels and still wait a week before adding fish. The other option is, if you have 2 filters on one tank, take one filter off and put in on the new tank and the new filter on the old tank. Once the new filter on the old tank has been established, then swap ....i hope that is clear :lol: cheers jk :thumbup: