Right now I have a 2.5 gallon tank, but my fish are outgrowing it so I am considering upgrading to a 6.5 gallon tank. However I want to do this with minimal stress to the fish. How can I ensure that as much of the beneficial bacteria from the old tank as possible goes into the new one? The new tank I am looking at has a built-in filter, so I won't be able to keep the same filter as the old tank. I have purchased a bottle of Nutrafin Cycle, but does it actually instantly cycle the tank?

Also, I currently have 1-week-old molly fry in the tank right now. What age should they be before I change the tank?

Thank you :)

If you move the old substrate and decor to the new tank, that will help.

I would personally run the old filter in the new tank along side the new filter, for at least 3 weeks.

As for the fry, if you can move over all the stuff as i said above, i would just move them with it.