I just did the same thing with a 30g long and a 10g. I pulled all the gravel from the 10 and put it in media bags, and put them in the 30, pulled the filter itself and put it behind the new filter in the 30, and placed all the plastic plants and rocks from the 10 and put them in the 30, with the same fish. Let it it run for a week and added 4 Tiger barbs (now there are 6 barbs and 1 Kenyi) and my levels have just been smooth as silk. Gotta love seeding a tank.