55 gallon is in my opinion not optimal size. Since, essentially the equipment needed would be the same as a size restriction from standard 55 - 120 gallon tank. In a 55 you lose so much in depth being such a narrow tank , making rockwork not very appealing. If water volume was an issue and you wanted to keep that down I would recommend a 75 gallon , at 48 inches long , 18.5 inches wide and 21 inches tall . This gives you more room front to back and better scapping options. The 90 gallon is the same as the 75 but about 4 inches taller . No real added benefit other than more water volume. A 110 gallon high would be like the 90 but comes in at 30 inches tall , no real added benefit again. The best option is the 120 if you wanted to go bigger. At 48.5 inches long and 24 inches deep and 25.5 inches tall , you get even more front to back space and the middle ground for height . That would be my choice if I had to stay in the 48 inch length but wanted a bigger tank . If you like the shallow lagoon style , deep blue makes a 80 gallon that is 48 by 24 inches deep and only 16 inches tall.
