my take is a 40G would be okay for a long time for an EBJD ... but once (if) it grows to 7" or more, you might want to consider a larger tank ...
I had to temporarily house a 7" port acara in a 36" wide tank, and in my opinion it just makes the tank look small ... I'd rather have the length of a 48" tank, so a 55G would be my preference ...
but yes, a 40G should be doable ... especially considering that JDs aren't big swimmers, mine tend to sit in the same spot for hours ...
I had to temporarily house a 7" port acara in a 36" wide tank, and in my opinion it just makes the tank look small ... I'd rather have the length of a 48" tank, so a 55G would be my preference ...
but yes, a 40G should be doable ... especially considering that JDs aren't big swimmers, mine tend to sit in the same spot for hours ...