i agree with just swap them over. tear down the 20, put fish in 1 bucket, plants in a bowl, and substrate in a bucket. drain tank and remove. set up new tank adding in substrate, plants, decor, fill with proper temp water, add fish. your plants,substrate etc already have good bacteria, so when moving them all over, all the bacteria go with them. just dont add a pile of new fish on day 1 of the new tank.