I will say no MBU get way to big for a 90 for any lenght of time.... I also do not think they need 800 gallons like you will here from a lot of people on here.
Basically speaking a 90G DEFINITELY will not work for with an MBU for life... considering even a Fahaka has a recommended tank size of no less than a 125G, so 90G for a MBU is a definite No No.... although personally speaking for an MBU i would go with nothing less than about 800G... but thats just me...