Correct me if I am wrong but a 55gal is 48 x 13 x 20 (I found that here http://www.marineland.com/sites/Marineland/Documents/Standard%20Aquarium%20Specs.pdf) and a 90 gal is 48 x 18 x 24.a blood needs a square cage to be able to streatch out COMPLEATLY and 2X as wide as its self and be able to turn around 55 not gonna work I know this because I have one a 55 gallon is 4x18x24