You know... I think we really need to stop talking in Gallons. Thats like talking in WPG (Watts per gallon) its out dated and honestly confuses people who don't know anything about footprint sizes for tanks..
I think in dealing with Large fish like anything in the ancient section, or some of the larger cichlids (Dovii, umbee) we should be speaking in footprint.
like, oh you need a 6'x2'x2' tank for that (Instead of calling it a 180)
I think it would clear up a lot of problems.
I mean this is the ultimate example..... Whats the difference between a 90g and a 100g....
90g 48 1/2 x 18 1/2 x 25 3/8
100g 72 1/2 x 18 1/2 x 19 3/8
You can CERTAINLY keep TOTALLY differen't fish in that 100g tank. Much, much more room.