beneficial bacteria builds up in your filter and on surfaces of tank so if you remove the water from the 55 and then fill the 90 and use your established filter plus adding prim to your tank its almost as if you have already cycled it al you really need in this case is to allow the filter to cycle the water in the new tank for about an hour or so but i would recommend using water from your previous set up too this way its almost as if all your doing is a water change because only about 15 to 30% of the water is new you could probably get away with up to 50% established water just add the new water gradually over an 8 to 24 houer time frame so as not to change the temp or chemistry in your tank to drastically for the fish