the diff between the 75 and 90 isnt the footprint, thats not why he said 90. the diff lies in water quality. it is easier to keep a 90 at good water quality than a 75 with the same 2 fish in there. it has the smaller footprint that makes it easier for people to accommodate but it is a larger volume so it makes it better quality water for the fish even if they dont have more swimming room.