Yeah that sounds spot on buddy my fella lives in a 8x2.5x2.5 and has done for around 2 years he's about 18" or so now maybe bigger not sure, when I go bigger I'll be going for length rather then more height or width as IME 2.5 (30") in enough in that regard as captive Dovii very very rarely exceed 20"-22" in home captivity, my next tank is likely to be 13x2.5x2.5 so he can get out his short bursts of pace better, with the longer length as my guy likes swimming very quickly up and down the length of the tank lol, he's an idiot lol