You shouldn't be asking what the minimum tank size is, you should be asking what size tank can house them comfortably for life. And the answer to that is way larger than 99% of the tanks people keep dovii in...
If you have to ask you should be keeping them. And even then...you probably shouldn't be keeping them. Mel's pair in a 600 gallon is a good starting point.
i agree and disagree...
most people ask the wrong questions...and most people can't house the fish they have or ask about for life...
however, asking doesn't disqualify him from keeping them... that's like when people asks how much it costs, and you reply 'if you have to ask you can't afford it.' ..... you have no idea of his financial status... maybe he can run out and build a 1000g tank on a whim and not flinch.