Would that be a generalized opinion? Would others see it that way too? I'm really curious about it. Because I have a 2.5 which i'm setting up and was thinking of adding a sump to it. Since water volume would be much more important in terms of breathing water for the fish rather than space. Something like that.....dont know how to explain it.....sorry. Anyway, with a sump, my 2.5 wouldnt be a 2.5 in terms of volume.....I dont want to be fooling myself...."I have a 2.5 (actually its not) gallon tank!" Pardon me for my unheard of questions.