ok , here's the easy way to establish a new tank.. take the filters off the established tank .. put them on the new tank, then put in the stock(fish) from the old tank .. there you go.. now add whatever new filtration you want to the new tank... but if the filters were good for the old tank/ stock it will work for the new tank..(bio) filtration is about load not tank size... make sure to test the new tank every few days .. this method is tried and true , but *nothing* is ever 100% , stuff happens...EDIT: if you are leaving fish in the old tank you obviously need to leave some filtration , so get other filtration established on the old tank (before you open the new tank, there are no shortcuts).. *if* all the fish are going to the new tank *take all the filtration to the new tank * and work "backwards" to establish the original tank as a "new tank"....